Mobile communication system, radio network controller, base station and user equipment

ABSTRACT

A mobile communication system includes a mobile station, a first base station and a second base station configured to perform radio communication with the mobile station, and a gateway station configured to perform communication with the first base station and the second base station or with the mobile station via the first base station and the second base station. One communication is performed between the mobile station and the gateway station by establishing a first communication connection between the gateway station and the first base station, a first radio communication connection between the first base station and the mobile station, and a second radio communication connection between the second base station and the mobile station. This enables a normal change of a cell during communication without any load on a network.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/431,965, filed Mar. 27, 2015, which is a National Stage ofInternational Application No., PCT/JP2013/005195, filed Sep. 3, 2013,and claims priority to Japanese Patent Application Nos., 2012-217229,filed Sep. 28, 2012 and 2013-028057, filed Feb. 15, 2013. The entirecontents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a mobile communication system includinga base station device and a communication terminal device configured toperform radio communication with the base station device.

BACKGROUND ART

Commercial service of a wideband code division multiple access (W-CDMA)system among so-called third-generation communication systems has beenoffered in Japan since 2001. In addition, high speed downlink packetaccess (HSDPA) service for achieving higher-speed data transmissionusing a downlink has been offered by adding a channel for packettransmission (high speed-downlink shared channel (HS-DSCH)) to thedownlink (dedicated data channel, dedicated control channel). Further,in order to increase the speed of data transmission in an uplinkdirection, service of a high speed uplink packet access (HSUPA) systemhas been offered. W-CDMA is a communication system defined by the 3rdgeneration partnership project (3GPP) that is the standard organizationregarding the mobile communication system, where the specifications ofRelease 10 version are produced.

Further, 3GPP is studying new communication systems referred to as longterm evolution (LTE) regarding radio sections and system architectureevolution (SAE) regarding the overall system configuration including acore network and a radio access network (hereinafter, also referred toas a network) as communication systems independent of W-CDMA. Thiscommunication system is also referred to as 3.9 generation (3.9 G)system.

In the LTE, an access scheme, a radio channel configuration, and aprotocol are totally different from those of the W-CDMA (HSDPA/HSUPA).For example, as to the access scheme, code division multiple access isused in the W-CDMA, whereas in the LTE, orthogonal frequency divisionmultiplexing (OFDM) is used in a downlink direction and single carrierfrequency division multiple access (SC-FDMA) is used in an uplinkdirection. In addition, the bandwidth is 5 MHz in the W-CDMA, while inthe LTE, the bandwidth can be selected from 1.4 MHz, 3 MHz, 5 MHz, 10MHz, 15 MHz, and 20 MHz per base station. Further, differently from theW-CDMA, circuit switching is not provided but a packet communicationsystem is only provided in the LTE.

In the LTE, a communication system is configured with a new core networkdifferent from the general packet radio service (GPRS) being the corenetwork of the W-CDMA, and thus, the radio access network of the LTE isdefined as a radio access network independent of the W-CDMA network.

Therefore, for differentiation from the W-CDMA communication system, acore network and a radio access network are referred to as an evolvedpacket core (EPC) and an evolved universal terrestrial radio accessnetwork (E-UTRAN), respectively, in the LTE communication system. Alsoin the radio access network, the base station that communicates with amobile terminal (user equipment (UE)) being a communication terminaldevice is referred to as an E-UTRAN NodeB (eNB). The EPC functions as aradio network controller that exchanges control data and user data witha plurality of base stations. The EPC is also referred to as an accessgateway (aGW). The system formed of the EPC and E-UTRAN is referred toas an evolved packet system (EPS).

Unicast service and evolved multimedia broadcast multicast service(E-MBMS service) are provided in the LTE communication system. TheE-MBMS service is broadcast multimedia service. The E-MBMS service ismerely referred to as MBMS in some cases. Bulk broadcast contents suchas news, weather forecast, and mobile broadcast are transmitted to aplurality of user equipments in the E-MBMS service. This is alsoreferred to as point to multipoint service.

Non-Patent Document 1 (Chapter 4) describes the current decisions by3GPP regarding an overall architecture in the LTE system. The overallarchitecture will be described with reference to FIG. 1. FIG. 1 is adiagram illustrating the configuration of the LTE communication system.With reference to FIG. 1, the E-UTRAN is composed of one or a pluralityof base stations 102, provided that a control protocol for a userequipment 101 such as a radio resource control (RRC), and user planessuch as a packet data convergence protocol (PDCP), radio link control(RLC), medium access control (MAC), or physical layer (PHY) are ended inthe base station 102.

The base stations 102 perform scheduling and transmission of a pagingsignal (also referred to as paging messages) notified from a mobilitymanagement entity (MME) 103. The base stations 102 are connected to eachother by means of an X2 interface. In addition, the base stations 102are connected to an evolved packet core (EPC) by means of an S1interface. More specifically, the base station 102 is connected to themobility management entity (MME) 103 by means of an S1_MME interface andconnected to a serving gateway (S-GW) 104 by means of an S1_U interface.

The MME 103 distributes the paging signal to a plurality of or a singlebase station 102. In addition, the MME 103 performs mobility control ofan idle state. When the user equipment is in the idle state and anactive state, the MME 103 manages a list of tracking areas.

The S-GW 104 transmits/receives user data to/from one or a plurality ofbase stations 102. The S-GW 104 serves as a local mobility anchor pointin handover between base stations. Moreover, a PDN gateway (P-GW) isprovided in the EPC. The P-GW performs per-user packet filtering andUE-ID address allocation.

The control protocol RRC between the user equipment 101 and the basestation 102 performs broadcast, paging, RRC connection management, andthe like. The states of the base station and the user equipment in RRCare classified into RRC_IDLE and RRC_CONNECTED. In RRC_IDLE, public landmobile network (PLMN) selection, system information (SI) broadcast,paging, cell reselection, mobility, and the like are performed. InRRC_CONNECTED, the user equipment has RRC connection and is capable oftransmitting/receiving data to/from a network. In RRC_CONNECTED, forexample, handover (HO) and measurement of a neighbour cell areperformed.

The current decisions by 3GPP regarding the frame configuration in theLTE system described in Non-Patent Document 1 (Chapter 5) will bedescribed with reference to FIG. 2. FIG. 2 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 2, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal (SS) per each radio frame. Thesynchronization signals are classified into a primary synchronizationsignal (P-SS) and a secondary synchronization signal (S-SS).

Multiplexing of channels for multimedia broadcast multicast servicesingle frequency network (MBSFN) and for non-MBSFN is performed on aper-subframe basis. MBSFN transmission is the simulcast transmissiontechnique realized by simultaneous transmission of the same waveformsfrom a plurality of cells. The MBSFN transmission from a plurality ofcells in the MBSFN area is seen as a single transmission by a userequipment. The MBSFN is a network that supports such MBSFN transmission.Hereinafter, a subframe for MBSFN transmission is referred to as MBSFNsubframe.

Non-Patent Document 2 describes a signaling example when MBSFN subframesare allocated. FIG. 3 is a diagram illustrating the configuration of theMBSFN frame. As shown in FIG. 3, the radio frames including the MBSFNsubframes are allocated per radio frame allocation period. The MBSFNsubframe is a subframe allocated for the MBSFN in a radio frame definedby the allocation period and the allocation offset (radio frameallocation offset), and serves to transmit multimedia data. The radioframe satisfying Equation (1) below is a radio frame including the MBSFNsubframes.

SFN mod radioFrameAllocationPeriod=radioFrameAllocationOffset  (1)

The MBSFN subframe is allocated with six bits. The leftmost bit definesthe MBSFN allocation for the second subframe (#1). The second bit, thirdbit, fourth bit, fifth bit, and sixth-bit from the left define the MBSFNallocation for the third subframe (#2), fourth subframe (#3), seventhsubframe (#6), eighth subframe (#7), and ninth subframe (#8),respectively. The case where the bit indicates “one” represents that thecorresponding subframe is allocated for the MBSFN.

Non-Patent Document 1 (Chapter 5) describes the current decisions by3GPP regarding the channel configuration in the LTE system. It isassumed that the same channel configuration is used in a closedsubscriber group (CSG) cell as that of a non-CSG cell. Physical channelsare described with reference to FIG. 4. FIG. 4 is a diagram illustratingphysical channels used in the LTE communication system.

With reference to FIG. 4, a physical broadcast channel (PBCH) 401 is achannel for downlink transmission from the base station 102 to the userequipment 101. A BCH transport block is mapped to four subframes withina 40 ms interval. There is no explicit signaling indicating 40 mstiming.

A physical control format indicator channel (PCFICH) 402 is a channelfor downlink transmission from the base station 102 to the userequipment 101. The PCFICH notifies the number of OFDM symbols used forPDCCHs from the base station 102 to the user equipment 101. The PCFICHis transmitted in each subframe.

A physical downlink control channel (PDCCH) 403 is a channel fordownlink transmission from the base station 102 to the user equipment101. The PDCCH notifies the resource allocation information for downlinkshared channel (DL-SCH) being one of the transport channels shown inFIG. 5 described below, resource allocation information for a pagingchannel (PCH) being one of the transport channels shown in FIG. 5, andhybrid automatic repeat request (HARD) information related to DL-SCH.The PDCCH carries an uplink scheduling grant. The PDCCH carriesacknowledgement (Ack)/negative acknowledgement (Nack) that is a responsesignal to uplink transmission. The PDCCH is referred to as an L1/L2control signal as well.

A physical downlink shared channel (PDSCH) 404 is a channel for downlinktransmission from the base station 102 to the user equipment 101. Adownlink shared channel (DL-SCH) that is a transport channel and a PCHthat is a transport channel are mapped to the PDSCH.

A physical multicast channel (PMCH) 405 is a channel for downlinktransmission from the base station 102 to the user equipment 101. Amulticast channel (MCH) that is a transport channel is mapped to thePMCH.

A physical uplink control channel (PUCCH) 406 is a channel for uplinktransmission from the user equipment 101 to the base station 102. ThePUCCH carries Ack/Nack that is a response signal to downlinktransmission. The PUCCH carries a channel quality indicator (CQI)report. The CQI is quality information indicating the quality ofreceived data or channel quality. In addition, the PUCCH carries ascheduling request (SR).

A physical uplink shared channel (PUSCH) 407 is a channel for uplinktransmission from the user equipment 101 to the base station 102. Anuplink shared channel (UL-SCH) that is one of the transport channelsshown in FIG. 5 is mapped to the PUSCH.

A physical hybrid ARQ indicator channel (PHICH) 408 is a channel fordownlink transmission from the base station 102 to the user equipment101. The PHICH carries Ack/Nack that is a response signal to uplinktransmission. A physical random access channel (PRACH) 409 is a channelfor uplink transmission from the user equipment 101 to the base station102. The PRACH carries a random access preamble.

A downlink reference signal (RS) is a known symbol in the LTEcommunication system. The following five types of downlink referencesignals are defined: cell-specific reference signals (CRS), MBSFNreference signals, data demodulation reference signal (DM-RS) beingUE-specific reference signals, positioning reference signals (PRS), andchannel-state information reference signals (CSI-RS). The physical layermeasurement objects of a user equipment include reference signalreceived power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)will be described with reference to FIG. 5. FIG. 5 is a diagramillustrating transport channels used in the LTE communication system.Part (A) of FIG. 5 shows mapping between downlink transport channels anddownlink physical channels. Part (B) FIG. 5 shows mapping between uplinktransport channels and uplink physical channels.

A broadcast channel (BCH) among the downlink transport channels shown inpart (A) of FIG. 5 is broadcast to the entire coverage of a base station(cell). The BCH is mapped to the physical broadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH can be broadcasted to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a user equipment for enabling the userequipment to save power. The DL-SCH is mapped to the physical downlinkshared channel (PDSCH).

The paging channel (PCH) supports DRX of the user equipment for enablingthe user equipment to save power. The PCH is required to broadcast tothe entire coverage of the base station (cell). The PCH is mapped tophysical resources such as the physical downlink shared channel (PDSCH)that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of MBMSservices (MTCH and MCCH) in multi-cell transmission. The MCH supportssemi-static resource allocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH) among the uplink transport channels shownin part (B) of FIG. 5. The UL-SCH supports dynamic or semi-staticresource allocation. The UL-SCH is mapped to the physical uplink sharedchannel (PUSCH).

A random access channel (RACH) shown in part (B) of FIG. 5 is limited tocontrol information. The RACH involves a collision risk. The RACH ismapped to the physical random access channel (PRACH).

The HARQ will be described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest (ARQ) and error correction (forward error correction). The HARQis advantageous in that error correction functions effectively byretransmission even for a channel whose communication quality changes.In particular, it is also possible to achieve further qualityimprovement in retransmission through combination of the receptionresults of the first transmission and the reception results of theretransmission.

An example of the retransmission method will be described. In the casewhere the receiver fails to successfully decode the received data, inother words, in the case where a cyclic redundancy check (CRC) erroroccurs (CRC=NG), the receiver transmits “Nack” to the transmitter. Thetransmitter that has received “Nack” retransmits the data. In the casewhere the receiver successfully decodes the received data, in otherwords, in the case where a CRC error does not occur (CRC=OK), thereceiver transmits “AcK” to the transmitter. The transmitter that hasreceived “Ack” transmits the next data.

Examples of the HARQ system include chase combining. In chase combining,the same data is transmitted in the first transmission andretransmission, which is the system for improving gains by combining thedata of the first transmission and the data of the retransmission inretransmission. Chase combining is based on the idea that correct datais partially included even if the data of the first transmissioncontains an error, and highly accurate data transmission is enabled bycombining the correct portions of the first transmission data and theretransmission data. Another example of the HARQ system is incrementalredundancy (IR). The IR is aimed to increase redundancy, where a paritybit is transmitted in retransmission to increase the redundancy bycombining the first transmission and retransmission, to thereby improvethe quality by an error correction function.

The logical channels described in Non-Patent Document 1 (Chapter 6) willbe described with reference to FIG. 6. FIG. 6 is a diagram illustratinglogical channels used in an LTE communication system. Part (A) of FIG. 6shows mapping between downlink logical channels and downlink transportchannels. Part (B) of FIG. 6 shows mapping between uplink logicalchannels and uplink transport channels.

A broadcast control channel (BCCH) is a downlink channel for broadcastsystem control information. The BCCH that is a logical channel is mappedto the broadcast channel (BCH) or downlink shared channel (DL-SCH) thatis a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging information and system information change notifications. The PCCHis used when the network does not know the cell location of a userequipment. The PCCH that is a logical channel is mapped to the pagingchannel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between user equipments and a base station. The CCCH is usedin the case where the user equipments have no RRC connection with thenetwork. In a downlink direction, the CCCH is mapped to the downlinkshared channel (DL-SCH) that is a transport channel. In an uplinkdirection, the CCCH is mapped to the uplink shared channel (UL-SCH) thatis a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to auser equipment. The MCCH is used only by a user equipment duringreception of the MBMS. The MCCH is mapped to the multicast channel (MCH)that is a transport channel.

A dedicated control channel (DCCH) is a channel that transmits dedicatedcontrol information between a user equipment and a network on apoint-to-point basis. The DCCH is used if the user equipment has an RRCconnection. The DCCH is mapped to the uplink shared channel (UL-SCH) inuplink and mapped to the downlink shared channel (DL-SCH) in downlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicated userequipment. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a user equipment. The MTCH is achannel used only by a user equipment during reception of the MBMS. TheMTCH is mapped to the multicast channel (MCH).

CGI represents a cell global identifier. ECGI represents an E-UTRAN cellglobal identifier. A closed subscriber group (CSG) cell is introduced inthe LTE, and the long term evolution advanced (LTE-A) and universalmobile telecommunication system (UMTS) described below. The CSG cellwill be described below (see Chapter 3.1 of Non-Patent Document 3).

The closed subscriber group (CSG) cell is a cell in which subscriberswho are allowed to use are specified by an operator (also referred to asa “cell for specific subscribers”). The specified subscribers areallowed to access one or more cells of a public land mobile network(PLMN). One or more cells in which the specified subscribers are allowedto access are referred to as “CSG cell(s).” Note that access is limitedin the PLMN.

The CSG cell is part of the PLMN that broadcasts a specific CSG identity(CSG ID; CSG-ID) and broadcasts “TRUE” in a CSG indication. Theauthorized members of the subscriber group who have registered inadvance access the CSG cells using the CSG-ID that is the accesspermission information.

The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDsexist in the LTE communication system. The CSG-IDs are used by userequipments (UEs) for making access from CSG-related members easier.

The locations of user equipments are tracked based on an area composedof one or more cells. The locations are tracked for enabling tracking ofthe locations of user equipments and calling user equipments, in otherwords, incoming calling to user equipments even in an idle state. Anarea for tracking locations of user equipments is referred to as atracking area.

The CSG whitelist is a list that may be stored in a universal subscriberidentity module (USIM) in which all CSG IDs of the CSG cells to whichthe subscribers belong are recorded. The CSG whitelist may be merelyreferred to as a whiltelist or an allowed CSG list as well. As to theaccess of user equipments through a CSG cell, the MME performs accesscontrol (see Chapter 4.3.1.2 of Non-Patent Document 4). Specificexamples of the access of user equipments include attach, combinedattach, detach, service request, and a tracking area update procedure(see Chapter 4.3.1.2 of Non-Patent Document 4).

The service types of a user equipment in an idle state will be describedbelow (see Chapter 4.3 of Non-Patent Document 3). The service types ofuser equipments in an idle state include a limited service, normalservice, and operator service. The limited service includes emergencycalls, earthquake and tsunami warning system (ETWS), and commercialmobile alert system (CMAS) on an acceptable cell described below. Thenormal service is a public service on a suitable cell described below.The operator service includes a service for operators only on a reservedcell described below.

A “suitable cell” will be described below. The “suitable cell” is a cellon which a UE may camp (Camp ON) to obtain normal service. Such a cellshall fulfill the following conditions (1) and (2).

(1) The cell is part of the selected PLMN or the registered PLMN, orpart of the PLMN of an “equivalent PLMN list”.

(2) According to the latest information provided by a non-access stratum(NAS), the cell shall further fulfill the following conditions (a) to(d):

(a) the cell is not a barred cell;

(b) the cell is part of a tracking area, not part of the list of“forbidden LAs for roaming”, where the cell needs to fulfill (1) above;

(c) the cell shall fulfill the cell selection criteria; and

(d) for a cell specified as CSG cell by system information (SI), theCSG-ID is part of a “CSG whitelist” of the UE, that is, is contained inthe CSG whitelist of the UE.

An “acceptable cell” will be described below. The “acceptable cell” isthe cell on which a UE may camp to obtain limited service. Such a cellshall fulfill the all following requirements (1) and (2).

(1) The cell is not a prohibited cell (also referred to as a “barredcell”).

(2) The cell fulfills the cell selection criteria.

“Barred cell” is indicated in the system information. “Reserved cell” isindicated in the system information.

“Camping on a cell” represents the state where a UE has completed thecell selection/cell reselection process and the UE has selected a cellfor monitoring the system information and paging information. The cellon which the UE camps may be referred to as a “serving cell”.

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation, or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 5 discloses three different modes ofthe access to the HeNB and HNB. Specifically, those are an open accessmode, a closed access mode, and a hybrid access mode.

The respective modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a CSG cell where only CSG members are allowedaccess. In the hybrid access mode, the HeNB and HNB are operated as CSGcells where non-CSG members are allowed access at the same time. Inother words, a cell in the hybrid access mode (also referred to as ahybrid cell) is the cell that supports both the open access mode and theclosed access mode.

In 3GPP, among all physical cell identities (PCIs), there is a range ofPCIs reserved by the network for use by CSG cells (see Chapter 10.5.1.1of Non-Patent Document 1). Division of the PCI range is also referred toas PCI split. The information about PCI split (also referred to as PCIsplit information) is broadcast in the system information from a basestation to user equipments being served thereby. To be served by a basestation means to take the base station as a serving cell.

Non-Patent Document 6 discloses the basic operation of a user equipmentusing PCI split. The user equipment that does not have the PCI splitinformation needs to perform cell search using all PCIs, for example,using all 504 codes. On the other hand, the user equipment that has thePCI split information is capable of performing cell search using the PCIsplit information.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Documents 7 and 8).

As to the LTE-A system, it is studied that a relay and a relay node (RN)are supported for achieving a high data rate, high cell-edge throughput,new coverage area, and the like. The relay node being a relay device iswirelessly connected to the radio-access network via a cell referred toas a donor cell (hereinafter, also referred to as a “Donor eNB; DeNB”).The network (NW)-to-relay node link shares the same frequency band withthe network-to-UE link within the range of the donor cell. In this case,the UE supporting Release 8 of 3GPP is also connectable to the donorcell. The link between a donor cell and a relay node is referred to as abackhaul link, and the link between the relay node and the UE isreferred to as an access link.

As the method of multiplexing a backhaul link in frequency divisionduplex (FDD), the transmission from a DeNB to an RN is performed at adownlink (DL) frequency band, and the transmission from an RN to a DeNBis performed at an uplink (UL) frequency band. As the method of dividingresources in a relay, a link from a DeNB to an RN and a link from an RNto a UE are time-division multiplexed at one frequency band, and a linkfrom an RN to a DeNB and a link from a UE to an RN are alsotime-division multiplexed at one frequency band. In a relay,accordingly, the transmission of the relay is prevented from interferingthe reception of its own relay.

Not only a normal eNB (macro cell) but also so-called local nodes suchas pico eNB (pico cell), HeNB (HNB, CSG cell), node for hotzone cells,relay node, remote radio head (RRH), and repeater are studied in 3GPP.The network composed of various types of cells as described above isalso referred to as a heterogeneous network (HetNet) in some cases.

The frequency bands (hereinafter, also referred to as “operating bands”)usable for communication have been predetermined in the LTE. Non-PatentDocument 9 describes the frequency bands.

Carrier aggregation (CA) is studied in the LTE-A system, in which two ormore component carriers (CCs) are aggregated to support widertransmission bandwidths up to 100 MHz.

A UE supporting Release 8 or 9 of 3GPP, which supports LTE, is capableof transmission and reception on only one CC corresponding to oneserving cell. Meanwhile, it is conceivable that a UE supporting Release10 of 3GPP may have the capability of transmission and reception, onlyreception, or only transmission on a plurality of CCs corresponding to aplurality of serving cells at the same time.

Each CC employs the configuration of Release 8 or 9 of 3GPP, and the CAsupports contiguous CCs, non-contiguous CCs, and CCs in differentfrequency bandwidths. The UE cannot configure uplink CCs (UL CCs) equalto or more than the number of downlink CCs (DL CCs). The CCs configuredby the same eNBs do not need to provide the same coverage. The CC iscompatible with Release 8 or 9 of 3GPP.

In CA, an independent HARQ entity is provided per serving cell in uplinkas well as downlink. A transport block is generated per TTI for eachserving cell. Each transport block and HARQ retransmission are mapped toa single serving cell.

In the case where CA is configured, a UE has single RRC connection witha NW. In RRC connection, one serving cell provides NAS mobilityinformation and security input. This cell is referred to as a primarycell (PCell). In downlink, a carrier corresponding to PCell is adownlink primary component carrier (DL PCC). In uplink, a carriercorresponding to PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a serving cell group witha PCell, in accordance with the UE capability. In downlink, a carriercorresponding to SCell is a downlink secondary component carrier (DLSCC). In uplink, a carrier corresponding to SCell is an uplink secondarycomponent carrier (UL SCC).

A serving cell group of one PCell and one or more SCells is configuredfor one UE.

The above-mentioned LTE Advanced (LTE-A) is studied as a furtheradvanced communication system regarding radio sections in 3GPP (seeNon-Patent Documents 7 and 8). The LTE-A is based on the LTEcommunication system regarding radio sections and is configured byaddition of several new techniques thereto. The new techniques includethe technique of supporting wider bands (wider bandwidth extension) andthe coordinated multiple point transmission and reception (CoMP)technique. The CoMP studied for LTE-A in 3GPP is described in Non-PatentDocument 10.

CoMP is the technique of expanding the coverage of high data rates,improving a cell-edge throughput, and increasing a communication systemthroughput by transmission or reception coordinated among multiplegeographically separated points. The CoMPs are grouped into downlinkCoMP (DL CoMP) and uplink CoMP (UL CoMP).

In DL CoMP, the PDSCH to one user equipment (UE) is transmitted incooperation among multiple points. The PDSCH to one UE may betransmitted from one point among multiple points or may be transmittedfrom points among multiple points. In DL CoMP, a serving cell refers toa single cell that transmits resource allocation over the PDCCH.

Joint processing (JP) and coordinated scheduling (CS)/coordinatedbeamforming (CB) (hereinafter, also referred to as “CS/CB”) are studiedas the DL CoMP method.

For JP, data is available at each point in a CoMP cooperating set. JPsare grouped into joint transmission (JT) and dynamic point selection(DPS). DPSs include dynamic cell selection (DCS). In JT, the PDSCH istransmitted from multiple points, specifically, part of or entire CoMPcooperating set, at a time. In DPS, the PDSCH is transmitted from onepoint in the CoMP cooperating set at a time.

In CS/CB, data is only available in transmission from a serving cell. InCS/CB, user scheduling or beamforming decisions are made withcoordination among cells corresponding to the CoMP cooperating set.

Base stations (NB, eNB, HNB, HeNB), remote radio unit (RRU), remoteradio equipment (RRE), remote radio head (RRH), relay node (RN), and thelike are studied as the units and cells that perform transmission andreception at multiple points. The unit and cell that perform coordinatedmultiple point transmission are also referred to as a multi-point unitand a multi-point cell, respectively.

3GPP is pursuing specifications standard of Release 12, where the use ofsmall eNBs (cells) is studied to satisfy a tremendous volume of trafficin the future. Examples of the study include the technique of increasingspectral efficiency through installation of a large number of small eNBs(cells) to increase communication capacity.

PRIOR ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: 3GPP TS 36.300 V11.2.0-   Non-Patent Document 2: 3GPP TS 36.331 V11.0.0-   Non-Patent Document 3: 3GPP TS 36.304 V11.0.0 Chapter 3.1, Chapter    4.3, Chapter 5.2.4-   Non-Patent Document 4: 3GPP TR 23.830 V9.0.0-   Non-Patent Document 5: 3GPP S1-083461-   Non-Patent Document 6: 3GPP R2-082899-   Non-Patent Document 7: 3GPP TR 36.814 V9.0.0-   Non-Patent Document 8: 3GPP TR 36.912 V10.0.0-   Non-Patent Document 9: 3GPP TS 36.819 V11.1.0-   Non-Patent Document 10: 3GPP TR 36.819 V11.0.0-   Non-Patent Document 11: 3GPP TR 23.401 V11.2.0-   Non-Patent Document 12: 3GPP RWS-120010-   Non-Patent Document 13: 3GPP RWS-120006-   Non-Patent Document 14: 3GPP TR 36.927 V10.1.0-   Non-Patent Document 15: 3GPP TS 36.141 V11.1.0

SUMMARY OF INVENTION Problems to be Solved by the Invention

In the small eNB (cell, base station), a procedure similar to thetypical procedure of changing a cell needs to be performed for handover.Unfortunately, this procedure needs control of both of U-plane andC-plane, resulting in many procedures. When a mobile station moves atsome speed in an area in which a plurality of small eNBs (cells) areconcentrated, a longer period of time for a handover procedure resultsin that the mobile station moves to a following cell area before thecompletion of the handover procedure. This leads to a problem that, forexample, handover cannot be performed appropriately. Further, in such acase, the occurrence frequency of handover increases to increase theprocesses associated with handover, placing a load on the network.

The present invention has an object to provide a communication systemenabling a normal change of a cell during communication without placinga load on a network even when high communication capacity is achievedthrough installation of, for example, a small eNB (cell).

Means to Solve the Problems

The present invention relates to a mobile communication system includinga mobile station, a first base station and a second base stationconfigured to perform radio communication with the mobile station, and agateway station configured to perform communication with the first basestation and the second base station or with the mobile station via thefirst base station and the second base station, wherein onecommunication is performed between the mobile station and the gatewaystation by establishing a first communication connection between thegateway station and the first base station, a first radio communicationconnection between the first base station and the mobile station, and asecond radio communication connection between the second base stationand the mobile station.

According to the present invention, one communication is performedbetween the mobile station and the gateway station by establishing thefirst communication connection between the gateway station and the firstbase station, the first radio communication connection between the firstbase station and the mobile station, and the second radio communicationconnection between the second base station and the mobile station. Thisenables a normal change of the base station during communication withoutany load on a network.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of an LTEcommunication system.

FIG. 2 is a diagram illustrating the configuration of a radio frame usedin the LTE communication system.

FIG. 3 is a diagram illustrating the configuration of an MBSFN frame.

FIG. 4 is a diagram illustrating physical channels used in the LTEcommunication system.

FIG. 5 is a diagram illustrating transport channels used in the LTEcommunication system.

FIG. 6 is a diagram illustrating logical channels used in the LTEcommunication system.

FIG. 7 is a block diagram showing the overall configuration of an LTEmobile communication system currently under discussion of 3GPP.

FIG. 8 is a block diagram showing the configuration of a user equipment71 of FIG. 7 being a user equipment according to the present invention.

FIG. 9 is a block diagram showing the configuration of a base station 72of FIG. 7 being a base station according to the present invention.

FIG. 10 is a block diagram showing the configuration of an MME unit 73of FIG. 7 being an MME according to the present invention.

FIG. 11 is a block diagram showing the configuration of a HeNBGW 74 ofFIG. 7 being a HeNBGW according to the present invention.

FIG. 12 is a flowchart showing an outline from a cell search to an idlestate operation performed by a user equipment (UE) in the LTEcommunication system.

Part (A) of FIG. 13 is an image diagram of a conventional cellconfiguration, part (B) of FIG. 13 is an image diagram showing downsizedcells, and part (C) of FIG. 13 is an image diagram showing macro eNBs(cells) and small eNBs (cells) that coexist.

FIG. 14 shows the architecture of a conventional EPS.

FIG. 15 shows the architecture of an EPS according to the firstembodiment.

FIG. 16 shows an example sequence of establishing communication andadding a cell initiated from a UE in this architecture.

FIG. 17 is a sequence diagram showing details of a service requestprocedure.

FIG. 18 is a sequence diagram showing details of a cell additionprocedure.

FIG. 19(A) shows an example sequence of adding an RRC Connection/S1bearer of an eNB#3 initiated from a UE.

FIG. 19(B) is a sequence diagram showing details of a cell additionprocedure.

FIG. 20 shows an example sequence of adding an RRC Connection/S1 bearerfor a target UE in accordance with the judgment by an eNB.

FIG. 21 shows an example sequence of adding an RRC Connection/S1 bearerfor a target UE in accordance with the judgment by an MME.

FIG. 22 shows an example sequence of releasing an RRC Connection/S1bearer of an eNB#1 initiated from a UE.

FIG. 23 shows an example sequence of releasing an RRC Connection/S1bearer of an eNB initiated from itself.

FIG. 24 shows an example sequence of releasing an RRC Connection/S1bearer of another eNB initiated from an eNB.

FIG. 25 shows an example sequence of releasing an RRC Connection/S1bearer of an eNB initiated from an MME.

FIG. 26 shows an example sequence of releasing an RRC Connection/S1bearer when time-out is detected.

FIG. 27(A) shows an example sequence of data forwarding in the casewhere a plurality of RRC Connection/S1 bearers are configured.

FIG. 27(B) is a sequence diagram showing details of a downlink trafficcontrol procedure.

FIG. 27(C) is a sequence diagram showing details of an uplink trafficcontrol procedure.

FIG. 28 shows the architecture of an EPS according to a secondembodiment.

FIG. 29 shows a protocol stack of an eNB according to the secondembodiment.

FIG. 30 shows an example sequence according to the second embodiment.

FIG. 31 shows an example sequence of releasing a U-plane establishingeNB according to the second embodiment.

FIG. 32 shows another example sequence of releasing a U-planeestablishing eNB according to the second embodiment.

FIG. 33 shows an example sequence of performing data forwarding betweenU-plane establishing eNBs according to the second embodiment.

FIG. 34 shows the architecture according to a first modification of thesecond embodiment.

FIG. 35 shows an example sequence according to the first modification ofthe second embodiment.

FIG. 36 shows the architecture according to a second modification of thesecond embodiment.

FIG. 37 shows an example sequence according to the second modificationof the second embodiment.

FIG. 38 shows an example sequence of establishing/modifying a DRB/S1bearer using a plurality of eNBs according to a third modification ofthe second embodiment.

FIG. 39 shows an example sequence of releasing a U-plane establishingeNB according to the third modification of the second embodiment.

FIG. 40 shows another example sequence of releasing a U-planeestablishing eNB according to the third modification of the secondembodiment.

FIG. 41 shows still another example sequence of releasing a U-planeestablishing eNB according to the third modification of the secondembodiment.

FIG. 42 shows the architecture in the case where an eNB dedicated forestablishing U-plane is configured according to a third embodiment.

FIG. 43 shows a protocol stack of an eNB according to the thirdembodiment.

FIG. 44 shows an example sequence of establishing/modifying a DRB usinga plurality of eNBs according to the third embodiment.

FIG. 45 shows an example sequence of releasing a U-plane establishingeNB according to the third embodiment.

FIG. 46 shows another example sequence of releasing a U-planeestablishing eNB according to the third embodiment.

FIG. 47 shows the architecture according to a first modification of thethird embodiment.

FIG. 48 is a conceptual diagram of a shared carrier according to a sixthembodiment.

FIG. 49 shows an example configuration of a shared carrier in the sameeNB.

FIG. 50 shows an example configuration of a shared carrier in differenteNBs.

FIG. 51 shows an example configuration in the case where a sharedcarrier is configured in a specific area.

FIG. 52 shows another example in the case where a shared carrier isconfigured in a specific area.

FIG. 53 shows the architecture according to a seventh embodiment.

FIG. 54 shows an example configuration of frames in accordance withschedulings performed by a MAC1 and a MAC2.

FIG. 55(A) shows an example sequence of a flow of establishingcommunication and transmitting data.

FIG. 55(B) shows details of a service request procedure.

FIG. 55(C) shows details of a DL scheduling/transmitting procedure.

FIG. 55(D) shows details of a UL scheduling/transmitting procedure.

FIG. 56 is a diagram for describing a conventional RLF-related process.

FIG. 57 is a diagram for describing an RLF-related process according toan eighth embodiment.

FIG. 58 shows an example sequence of the RLF-related process accordingto the eighth embodiment.

FIG. 59 shows an example sequence of a process [A] in FIG. 58.

FIG. 60 shows another example sequence of the process [A] in FIG. 58.

FIG. 61 shows an example sequence of a process [B] in FIG. 58.

FIG. 62 shows an example sequence of a process [C] in FIG. 58.

FIG. 63 is a diagram for describing an RLF-related process according toa ninth embodiment.

FIG. 64 shows an example sequence of an RLF-related process by a U-planeonly establishing cell according to the ninth embodiment.

FIG. 65 is a diagram illustrating the case in which a plurality of eNBsare treated as one group.

FIG. 66 is a diagram illustrating the case in which communication isperformed using a macro cell and a plurality of small cells positionallyoverlaid on the macro cell and CA is performed in the macro cell.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 7 is a block diagram showing an overall configuration of an LTEcommunication system, which is currently under discussion of 3GPP. 3GPPis studying an overall configuration of a system including closedsubscriber group (CSG) cells (Home-eNodeBs (Home-eNB; HeNB) of E-UTRAN,Home-NB (HNB) of UTRAN) and non-CSG cells (eNodeB (eNB) of E-UTRAN,NodeB (NB) of UTRAN, and BSS of GERAN) and, as to E-UTRAN, proposes theconfiguration as shown in FIG. 7 (see Chapter 4.6.1 of Non-PatentDocument 1).

FIG. 7 will be described. A mobile terminal device (hereinafter,referred to as a “user equipment” or “UE”) 71 being a communicationterminal device is capable of performing radio communication with a basestation device (hereinafter, referred to as a “base station”) 72 andtransmits/receives signals through radio communication. The basestations 72 are classified into an eNB 72-1 and a Home-eNB 72-2.

The eNB 72-1 is connected to an MME/S-GW unit (hereinafter, alsoreferred to as an “MME unit”) 73 including an MME, S-GW, or MME and S-GWthrough an S1 interface, and control information is communicated betweenthe eNB 72-1 and the MME unit 73. A plurality of MME units 73 may beconnected to one eNB 72-1. The MME unit 73 is equivalent to managementmeans. The MME unit 73 is included in an EPC being a core network. TheeNBs 72-1 are connected to each other by means of an X2 interface, andcontrol information is communicated between the eNBs 72-1.

The Home-eNB 72-2 is connected to the MME unit 73 by means of an S1interface, and control information is communicated between the Home-eNB72-2 and the MME unit 73. A plurality of Home-eNBs 72-2 are connected toone MME unit 73. Or, the Home-eNBs 72-2 are connected to the MME units73 through a Home-eNB gateway (HeNBGW) 74. The Home-eNBs 72-2 areconnected to the HeNBGW 74 by means of the S1 interface, and the HeNBGW74 is connected to the MME units 73 through an S1 interface.

One or a plurality of Home-eNBs 72-2 are connected to one HeNBGW 74, andinformation is communicated therebetween through an S1 interface. TheHeNBGW 74 is connected to one or a plurality of MME units 73, andinformation is communicated therebetween through an S1 interface.

The MME units 73 and HeNBGW 74 are devices of higher nodes and controlthe connection between the user equipment (UE) 71 and the eNB 72-1 orHome-eNB 72-2 being a base station. The MME units 73, specifically, theMME and S-GW constituting the MME unit 73 and the HeNBGW 74 areequivalent to management means. The MME units 73 and HeNBGW are includedin the EPC being a core network.

Further, 3GPP is currently studying the configuration below. The X2interface between the Home-eNBs 72-2 is supported. In other words, theHome-eNBs 72-2 are connected to each other by means of an X2 interface,and control information is communicated between the Home-eNBs 72-2. TheHeNBGW 74 appears to the MME unit 73 as the eNB 72-1. The HeNBGW 74appears to the Home-eNB 72-2 as the MME unit 73.

The interfaces between the Home-eNBs 72-2 and the MME units 73 are thesame, which are the S1 interfaces, in both cases where the Home-eNB 72-2is connected to the MME unit 73 through the HeNBGW 74 and it is directlyconnected to the MME unit 73. The HeNBGW 74 does not support themobility to the Home-eNB 72-2 or the mobility from the Home-eNB 72-2that spans a plurality of MME units 73. The Home-eNB 72-2 constitutesand supports a single cell.

The base station device supports a single cell alone, such as theHome-eNB 72-2, which is not limited thereto. One base station device maysupport a plurality of cells. In the case where one base station devicesupports a plurality of cells, every cell is configured to communicatewith a mobile terminal.

FIG. 8 is a block diagram showing the configuration of the userequipment 71 of FIG. 7 being a user equipment according to the presentinvention. The transmission process of the user equipment 71 shown inFIG. 8 will be described. First, a transmission data buffer unit 803stores the control data from a protocol processing unit 801 and the userdata from an application unit 802. The data stored in the transmissiondata buffer unit 803 is passed to an encoding unit 804 and is subjectedto an encoding process such as error correction. There may exist thedata output from the transmission data buffer unit 803 directly to amodulating unit 805 without the encoding process. The data encoded bythe encoding unit 804 is modulated by the modulating unit 805. Themodulated data is output to a frequency converting unit 806 after beingconverted into a baseband signal, and is then converted into a radiotransmission frequency. After that, a transmission signal is transmittedfrom an antenna 807 to the base station 72.

The user equipment 71 executes the reception process as follows. Theradio signal is received through the antenna 807 from the base station72. The received signal is converted from a radio reception frequencyinto a baseband signal by the frequency converting unit 806 and is thendemodulated by a demodulating unit 808. The demodulated data is passedto a decoding unit 809 and is subjected to a decoding process such aserror correction. Among the pieces of decoded data, the control data ispassed to the protocol processing unit 801, while the user data ispassed to the application unit 802. A series of processes of the userequipment 71 is controlled by a control unit 810. This means that,though not shown in FIG. 8, the control unit 810 is connected to therespective units 801 to 809.

FIG. 9 is a block diagram showing the configuration of the base station72 of FIG. 7 being a base station according to the present invention.The transmission process of the base station 72 shown in FIG. 9 will bedescribed. An EPC communication unit 901 performs data transmission andreception between the base station 72 and the EPCs (such as MME unit 73and HeNBGW 74). A communication with another base station unit 902performs data transmission and reception to/from another base station.The EPC communication unit 901 and the communication with another basestation unit 902 respectively transmit and receive information to/from aprotocol processing unit 903. The control data from the protocolprocessing unit 903, and the user data and control data from the EPCcommunication unit 901 and the communication with another base stationunit 902 are stored in a transmission data buffer unit 904.

The data stored in the transmission data buffer unit 904 is passed to anencoding unit 905 and is then subjected to an encoding process such aserror correction. There may exist the data output from the transmissiondata buffer unit 904 directly to a modulating unit 906 without theencoding process. The encoded data is modulated by the modulating unit906. The modulated data is output to a frequency converting unit 907after being converted into a baseband signal, and is then converted intoa radio transmission frequency. After that, a transmission signal istransmitted from an antenna 908 to one or a plurality of user equipments71.

The reception process of the base station 72 is executed as follows. Aradio signal from one or a plurality of user equipments 71 is receivedthrough the antenna 908. The received signal is converted from a radioreception frequency into a baseband signal by the frequency convertingunit 907, and is then demodulated by a demodulating unit 909. Thedemodulated data is passed to a decoding unit 910 and is then subjectedto a decoding process such as error correction. Among the pieces ofdecoded data, the control data is passed to the protocol processing unit903, EPC communication unit 901, or communication with another basestation unit 902, while the user data is passed to the EPC communicationunit 901 and the communication with another base station unit 902. Aseries of processes by the base station 72 is controlled by a controlunit 911. This means that, though not shown in FIG. 9, the control unit911 is connected to the respective units 901 to 910.

The communication with another base station unit 902 is equivalent to anotification unit and an acquisition unit. The transmission data bufferunit 904, the encoding unit 905, the modulating unit 906, the frequencyconverting unit 907, the antenna 908, the demodulating unit 909, and thedecoding unit 910 are equivalent to a communication unit.

The functions of the Home-eNB 72-2 currently under discussion of 3GPPwill be described below (see Chapter 4.6.2 of Non-Patent Document 1).The Home-eNB 72-2 has the same function as that of the eNB 72-1. Inaddition, the Home-eNB 72-2 has the function of discovering a suitableserving HeNBGW 74 in the case of connection to the HeNBGW 74. TheHome-eNB 72-2 is connected only to one HeNBGW 74. That is, in the caseof the connection to the HeNBGW 74, the Home-eNB 72-2 does not use theFlex function in the S1 interface. When the Home-eNB 72-2 is connectedto one HeNBGW 74, it is not simultaneously connected to another HeNBGW74 or another MME unit 73.

The tracking area code (TAC) and PLMN ID of the Home-eNB 72-2 aresupported by the HeNBGW 74. When the Home-eNB 72-2 is connected to theHeNBGW 74, selection of the MME unit 73 at “UE attachment” is performedby the HeNBGW 74 instead of by the Home-eNB 72-2. The Home-eNB 72-2 maybe deployed without network planning. In this case, the Home-eNB 72-2 ismoved from one geographical area to another geographical area. TheHome-eNB 72-2 in this case is accordingly required to be connected to adifferent HeNBGW 74 depending on its location.

FIG. 10 is a block diagram showing the configuration of the MMEaccording to the present invention. FIG. 10 shows the configuration ofan MME 73 a included in the MME unit 73 shown in FIG. 7 described above.A PDN GW communication unit 1001 performs data transmission andreception between the MME 73 a and a PDN GW. A base stationcommunication unit 1002 performs data transmission and reception betweenthe MME 73 a and the base station 72 by means of the S1 interface. Inthe case where the data received from the PDN GW is user data, the userdata is passed from the PDN GW communication unit 1001 to the basestation communication unit 1002 through a user plane communication unit1003 and is then transmitted to one or a plurality of base stations 72.In the case where the data received from the base station 72 is userdata, the user data is passed from the base station communication unit1002 to the PDN GW communication unit 1001 through the user planecommunication unit 1003 and is then transmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is passed from the PDN GW communication unit 1001 to acontrol plane control unit 1005. In the case where the data receivedfrom the base station 72 is control data, the control data is passedfrom the base station communication unit 1002 to the control planecontrol unit 1005.

A HeNBGW communication unit 1004 is provided in the case where theHeNBGW 74 is provided, which performs data transmission and reception ofthe interface (IF) between the MME 73 a and the HeNBGW 74 according toan information type. The control data received from the HeNBGWcommunication unit 1004 is passed from the HeNBGW communication unit1004 to the control plane control unit 1005. The processing results ofthe control plane control unit 1005 are transmitted to the PDN GWthrough the PDN GW communication unit 1001. The processing results ofthe control plane control unit 1005 are transmitted to one or aplurality of base stations 72 by means of the S1 interface through thebase station communication unit 1002, and are transmitted to one or aplurality of HeNBGWs 74 through the HeNBGW communication unit 1004.

The control plane control unit 1005 includes a NAS security unit 1005-1,an SAE bearer control unit 1005-2, an idle state mobility managing unit1005-3, and other unit, and performs an overall process for the controlplane. The NAS security unit 1005-1 provides, for example, security of anon-access stratum (NAS) message. The SAE bearer control unit 1005-2manages, for example, a system architecture evolution (SAE) bearer. Theidle state mobility managing unit 1005-3 performs, for example, mobilitymanagement of an idle state (LTE-IDLE state, which is merely referred toas idle as well), generation and control of a paging signal in an idlestate, addition, deletion, update, and search of a tracking area of oneor a plurality of user equipments 71 being served thereby, and trackingarea list management.

The MME 73 a begins a paging protocol by transmitting a paging messageto the cell belonging to a tracking area in which the UE is registered.The idle state mobility managing unit 1005-3 may manage the CSG of theHome-eNBs 72-2 to be connected to the MME 73 a, CSG-IDs, and awhitelist.

In the CSG-ID management, the relationship between a user equipmentcorresponding to the CSG-ID and the CSG cell is managed (for example,added, deleted, updated, or searched). For example, the relationship maybe the relationship between one or a plurality of user equipments whoseuser access registration has been performed with a CSG-ID and the CSGcells belonging to this CSG-ID. In the whitelist management, therelationship between the user equipment and the CSG-ID is managed (forexample, added, deleted, updated, or searched). As an example, one or aplurality of CSG-IDs with which user registration has been performed bya user equipment may be stored in the whitelist. The above-mentionedmanagement related to the CSG may be performed by another part of theMME 73 a. A series of processes by the MME 73 a is controlled by acontrol unit 1006. This means that, though not shown in FIG. 10, thecontrol unit 1006 is connected to the respective units 1001 to 1005.

The function of the MME 73 a currently under discussion of 3GPP will bedescribed below (see Chapter 4.6.2 of Non-Patent Document 1). The MME 73a performs access control for one or a plurality of user equipmentsbeing members of closed subscriber groups (CSGs). The MME 73 arecognizes the execution of paging optimization as an option.

FIG. 11 is a block diagram showing the configuration of the HeNBGW 74 ofFIG. 7 being a HeNBGW according to the present invention. An EPCcommunication unit 1101 performs data transmission and reception betweenthe HeNBGW 74 and the MME 73 a by means of the S1 interface. A basestation communication unit 1102 performs data transmission and receptionbetween the HeNBGW 74 and the Home-eNB 72-2 by means of the S1interface. A location processing unit 1103 performs the process oftransmitting, to a plurality of Home-eNBs 72-2, the registrationinformation or the like among the data transmitted from the MME 73 athrough the EPC communication unit 1101. The data processed by thelocation processing unit 1103 is passed to the base stationcommunication unit 1102 and is passed to one or a plurality of Home-eNBs72-2 through the S1 interface.

The data only caused to pass through (to be transparent) withoutrequiring the process by the location processing unit 1103 is passedfrom the EPC communication unit 1101 to the base station communicationunit 1102, and is transmitted to one or a plurality of Home-eNBs 72-2through the S1 interface. A series of processes by the HeNBGW 74 iscontrolled by a control unit 1104. This means that, though not shown inFIG. 11, the control unit 1104 is connected to the respective units 1101to 1103.

The function of the HeNBGW 74 currently under discussion of 3GPP will bedescribed below (see Chapter 4.6.2 of Non-Patent Document 1). The HeNBGW74 relays an S1 application. The HeNBGW 74 ends the S1 application thatis not associated with the user equipment 71 though it is a part of theprocedures toward the Home-eNB 72-2 and towards the MME 73 a. When theHeNBGW 74 is deployed, the procedure that is not associated with theuser equipment 71 is communicated between the Home-eNB 72-2 and theHeNBGW 74 and between the HeNBGW 74 and the MME 73 a. The X2 interfaceis not set between the HeNBGW 74 and another node. The HeNBGW 74recognizes the execution of paging optimization as an option.

An example of a cell search method in a mobile communication system willbe described next. FIG. 12 is a flowchart showing an outline from a cellsearch to an idle state operation performed by a user equipment (UE) inthe LTE communication system. When starting a cell search, in StepST1201, the user equipment synchronizes the slot timing and frame timingby a primary synchronization signal (P-SS) and a secondarysynchronization signal (S-SS) transmitted from a neighbor base station.

The P-SS and S-SS are collectively referred to as a synchronizationsignal (SS). Synchronization codes, which individually correspond tophysical cell identities (PCIs) assigned per cell, are assigned to thesynchronization signal (SS). The number of PCIs is currently studied in504 ways. These 504 ways are used for synchronization, and the PCIs ofthe synchronized cells are detected (specified).

In Step ST1202, next, the user equipment detects a cell-specificreference signal (CRS) being a reference signal (RS) transmitted fromthe base station per cell and measures the reference signal receivedpower (RSRP). The codes individually corresponding to the PCIs are usedfor the reference signal RS. Separation from another cell is enabled bycorrelation using the code. The code for RS of the cell is derived fromthe PCI specified in Step ST1201, which makes it possible to detect theRS and measure the RS received power.

In Step ST1203, next, the user equipment selects the cell having thebest RS reception quality, for example, cell having the highest RSreceived power, that is, best cell, from one or more cells that havebeen detected up to Step ST1202.

In Step ST1204, next, the user equipment receives the PBCH of the bestcell and obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas transmission bandwidth configuration (dl-bandwidth)), the number oftransmission antennas, and system frame number (SFN).

In Step ST1205, next, the user equipment receives the DL-SCH of the cellbased on the cell configuration information of the MIB, to therebyobtain a system information block (SIB) 1 of the broadcast informationBCCH. The SIB1 contains the information about the access to the cell,information on cell selection, and scheduling information about otherSIB (SIBk; k is an integer equal to or larger than two). In addition,the SIB1 contains a tracking area code (TAC).

In Step ST1206, next, the user equipment compares the TAC of the SIB1received in Step ST1205 with the TAC portion of a tracking area identity(TAI) in the tracking area list that has already been possessed by theuser equipment. The tracking area list is also referred to as a TAIlist. TAI is a TA identity and is formed of a mobile country code (MCC),a mobile network code (MNC), and a tracking area code (TAC). MCC is acountry code. MNC is a network code. TAC is a TA code number.

In the case where the TAC received in Step ST1205 is identical to theTAC included in the tracking area list as a result of the comparison ofStep ST1206, the user equipment enters an idle state operation in thecell. In the case where the TAC received in Step ST1205 is not includedin the tracking area list as a result of the comparison, the userequipment requires a core network (EPC) including MME and the like tochange a tracking area through the cell for performing tracking areaupdate (TAU).

The core network updates the tracking area list based on anidentification number (such as a UE-ID) of the user equipmenttransmitted from the user equipment together with a TAU request signal.The core network transmits the updated tracking area list to the userequipment. The user equipment rewrites (updates) the TAC list of theuser equipment based on the received tracking area list. After that, theuser equipment enters the idle state operation in the cell.

In the LTE, LTE-A, and universal mobile telecommunication system (UMTS),the introduction of a closed subscriber group (CSG) cell is studied. Asdescribed above, access is allowed for only one or a plurality of userequipments registered with the CSG cell. A CSG cell and one or aplurality of user equipments registered with the CSG cell constitute oneCSG. A specific identification number referred to as CSG-ID is added tothe thus constituted CSG. One CSG may contain a plurality of CSG cells.After being registered with any one of the CSG cells, the user equipmentcan access another CSG cell of the CSG to which the registered CSG cellbelongs.

Alternatively, the Home-eNB in the LTE and LTE-A and the Home-NB in theUMTS are used as the CSG cell in some cases. The user equipmentregistered with the CSG cell has a whitelist. Specifically, thewhitelist is stored in the subscriber identity module (SIM) or USIM. Thewhitelist stores the CSG information of the CSG cell with which the userequipment has been registered. Specific examples of the CSG informationmay include CSG-ID, tracking area identity (TAI), and TAC. Any one ofthe CSG-ID and TAC is adequate as long as they are associated with eachother. Alternatively, ECGI is adequate as long as the CSG-ID and TAC areassociated with ECGI.

As can be seen from the above, the user equipment that has no whitelist(including a case where the whitelist is empty in the present invention)is not allowed to access the CSG cell but is allowed to access thenon-CSG cell only. On the other hand, the user equipment which has awhitelist is allowed to access the CSG cell of the CSG-ID with whichregistration has been performed as well as the non-CSG cell.

The HeNB and HNB are required to support various services. For example,in certain service, an operator causes the predetermined HeNB and HNB toregister user equipments therein and permits only the registered userequipments to access the cells of the HeNB and HNB, which increasesradio resources available for the user equipments and enables high-speedcommunication. The operator correspondingly sets a high charge comparedwith a normal service.

In order to achieve the above-mentioned service, the closed subscribergroup (CSG) cell accessible only to the registered (subscribed ormember) user equipments is introduced. A large number of closedsubscriber group (CSG) cells are required to be installed in shoppingmalls, apartment buildings, schools, companies, and the like. Forexample, the following manner of use is required: the CSG cells areinstalled for each store in shopping malls, for each room in apartmentbuildings, for each classroom in schools, and for each section incompanies such that only the users who have registered with therespective CSG cells are permitted to use those CSG cells.

The HeNB/HNB is required not only to complement the communication out ofthe coverage of the macro cell (area complementing HeNB/HNB) but also tosupport various services as described above (service providingHeNB/HNB). This also leads to a case where the HeNB/HNB is installedwithin the coverage of the macro cell.

Widespread use of smartphones and tablet terminals explosively increasestraffic in cellular radio communications, causing a fear of insufficientradio resources all over the world. To increase spectral efficiencyagainst this fear, it is studied to downsize cells such that the cellsare spatially separated.

Part (A) of FIG. 13 is an image diagram of a conventional cellconfiguration. 1301 denotes the coverage configured by a macro eNB(cell). The macro eNB (cell) configures a relatively wide rangecoverage. Conventionally, a relatively wide range coverage configured bya plurality of macro eNBs (cells) covers an area.

Part (B) of FIG. 13 is an image diagram of downsized cells. 1302 denotesthe coverage configured by a small eNB (cell). The small eNB (cell)configures a narrow range coverage compared with the macro eNB (cell).Thus, a larger number of small eNBs (cells) are required to cover acoverage than in a conventional case.

Part (C) of FIG. 13 is an image diagram of macro eNBs (cells) and smalleNBs (cells) that coexist. 1303 denotes the coverage configured by themacro eNB (cell), and 1304 denotes the coverage configured by the smalleNB (cell). With reference to part (C) of FIG. 13, the coverage of oneeNB (cell) is included in the coverage of another eNB (cell) in somecases. As described above, the coverage of a macro eNB (cell) and thecoverage of a small eNB (cell) may overlap each other in a complicatedmanner or may not overlap each other. Further, a large number of smalleNBs (cells) may be configured in the coverage of one macro eNB (cell).

Hereinafter, description will be given of the case in which a pluralityof small eNBs (cells) are configured in a system as shown in part (B) ofFIG. 13 and part (C) of FIG. 13.

FIG. 14 shows the architecture of a conventional EPS. 1401 denotes aP-GW; 1402, an MME; 1403, an S-GW; 1404, an eNB; and 1405, a UE. 1406denotes an interface (S5) between the P-GW and the S-GW; 1407, aninterface (S11) between the MME and the S-GW; 1408, an interface(S1-MME) between the MME and the eNB; 1409, an interface (S1-U) betweenthe S-GW and the eNB; and 1410, an interface (Uu) between the eNB andthe UE. The solid line denotes an interface that supports user traffic(U-plane), and the dashed line denotes an interface that supportssignaling (C-plane). The S5 interface 1406 and the Uu interface 1410support both of the user traffic and the signaling. As shown in thefigure, in the conventional EPS, C-plane and U-plane communications areperformed using one eNB for one communication with a UE being acommunication target. In other words, one eNB is used to establish oneRRC connection/S1 bearer.

The problem to be solved in the first embodiment will be describedbelow. Also in a small cell, a procedure similar to a typical procedurefor a cell change described in Chapter 10.1.2 of Non-Patent Document 1(TS36.300) needs to be performed for a change (handover) of a cellduring communication. However, this needs control of both of U-plane andC-plane, leading to increased procedures, as described in Chapter 10.1.2of Non-Patent Document 1 (TS36.300). When the UE moves at some speed inan area where a plurality of small cells are concentrated, if a handoverprocedure is time-consuming, the UE moves to a following cell areabefore the completion of the handover procedure, causing a problem thathandover cannot be performed appropriately. In such a case, a change(handover) of a cell during communication occurs at high frequency toconsiderably increase associated processes, placing a load on thenetwork.

The solution in the first embodiment will be described below. To solvethe above-mentioned problem, it is made possible to establish aplurality of RRC connections/S1 bearers for one communication, enablinga cell change without the procedure for a cell change of Chapter 10.1.2of Non-Patent Document 1 (TS36.300).

FIG. 15 shows the architecture of an EPS according to the firstembodiment. With reference to FIG. 15, a UE (1501) establishes RRCconnection with three eNBs (an eNB#1 (1502), an eNB#2 (1503), and aneNB#3(1504)), and each eNB establishes an S1 bearer with one S-GW. Here,an MME (1505) notifies the data allocation method and associatedparameters based on the delivery confirmation result at Uu, the qualityinformation, the information on arrival of a reception wave, the UElocation information, or the like. Specific examples of the deliveryconfirmation result include Ack/Nack of HARQ and Ack/Nack of ARQ in RLC.Specific examples of the quality information include CQI and CSI. Aspecific example of the information on arrival of a reception wave is anangle of arrival (AoA). A specific example of the UE locationinformation is the UE positioning estimation result.

Here, the UE (1501) corresponds to a mobile station; the eNB#1 (1502), afirst base station; the eNB#2 (1503), a second base station; and the MME(1505) and the S-GW (1506), a gateway station. For C-plane signals, theRRC connection between the UE (1501) and the eNB#1 (1502) corresponds toa first radio communication connection, and the RRC connection betweenthe UE (1501) and the eNB#2 (1503) corresponds to a second radiocommunication connection. Similarly, for C-plane signals, the S1-MMEsignaling connection between the MME (1505) and the eNB#1 (1502)corresponds to a first communication connection, and the S1-MMEsignaling connection between the MME (1505) and the eNB#2 (1503)corresponds to a second communication connection. For U-plane signals,the radio bearer between the UE (1501) and the eNB#1 (1502) correspondsto a first radio communication connection, and the radio bearer betweenthe UE (1501) and the eNB#2 (1503) corresponds to a second radiocommunication connection. Similarly, for U-plane signals, the S1 bearerbetween the S-GW (1506) and the eNB#1 (1502) corresponds to a firstcommunication connection, and the S1 bearer between the S-GW (1506) andthe eNB#2 (1503) corresponds to a second communication connection.

As described above, one communication is performed between the mobilestation and the gateway station by establishing the first communicationconnection between the gateway station and the first base station, thesecond communication connection between the gateway station and thesecond base station, the first radio communication connection betweenthe first base station and the mobile station, and the second radiocommunication connection between the second base station and the mobilestation. A cell change is accordingly enabled through addition orrelease of the communication connection or the radio communicationconnection.

The U-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and a second path including the secondcommunication connection and the second radio communication connection.The C-plane signals are transmitted while being distributed to the firstpath including the first communication connection and the first radiocommunication connection and a second path including the secondcommunication connection and the second radio communication connection.

The S-GW (1506) transmits data while dividing the data on a per-packetbasis to a plurality of eNBs whose RRC Connection/S1 bearer has beenestablished. The packet is, for example, an internet protocol (IP)packet. The above-mentioned basis is made to coincide with thecommunication basis in terminals that perform IP communication toeliminate the need for dividing packets, improving transmissionefficiency. 1507 to 1509 denote U-plane/C-plane channels for the eNB#1to the eNB#3 at Uu. 1511, 1513, and 1515 denote U-plane channels betweenthe S-GW and the eNB#1, between the S-GW and the eNB#2, and between theS-GW and the eNB#3. 1512, 1514, and 1516 denote C-plane channels betweenthe MME and the eNB#1 to eNB#3.

The RRC connection/S1 bearer with a plurality of eNBs can be establishedfor one communication in a specific area, the specific area being, forexample, the area in the same TA, the same MME, or the same S-GW.Setting a specific area as the area in the same MME or the same TAallows for concentrated control in communication control, simplifyingcommunication control. Setting a specific area as the area in the sameS-GW allows U-plane data to be allocated at a place close to theE-UTRAN, simplifying path control.

A change of a cell during communication in the specific area does notinvolve a handover procedure and is performed through the addition andrelease of an RRC Connection/S1 bearer.

FIG. 16 shows an example sequence of establishing communication andadding a cell initiated from a UE in the architecture. The sequenceincludes Step ST1815 that is Service Request Procedure (plural RRC) forfirst establishing a bearer and Step ST1637 that is Cell AdditionProcedure (addition of eNB#2) that is a cell addition procedure(addition of eNB#2) of adding an RRC Connection/S1 bearer of the eNB#2to the established bearer.

In Step ST1815 that is the Service Request Procedure (plural RRC), theUE that has established a bearer detects and monitors neighbor cells asin a normal communication operation. In Step ST1636, the UE judgeswhether to add a target eNB using the detection and monitoring results.

As the method for the judgment, for example, judgment is made inaccordance with whether the quality of a reference signal of a monitoredcell exceeds a set threshold with respect to the current level of a cellor whether a calculated distance between the location informationmeasured by the UE and the location information of the eNB obtained inadvance by any method falls within a set threshold. Specific examples ofthe reference signal include a tracking RS, a demodulation RS, a CRS,and a UE-specific RS. As the method of obtaining the locationinformation of an eNB in advance, the eNB may include the locationinformation of the own eNB in system information and then broadcast thesystem information or may notify the UE of the location informationthrough RRC signaling.

If it is judged that addition is required in the judgment for addition,Step ST1637 that is Cell Addition Procedure (addition of eNB#2) isperformed.

FIG. 17 is a sequence diagram showing details of the service requestprocedure. Service Request Procedure (plural RRC) is based on the UEtriggered Service Request procedure described in Chapter 5.3.4.1 ofNon-Patent Document 11 (TS23.401). After the S-GW transmits ModifyBearer Response (UEID, bearer info) to the MME in Step ST1833, in StepST1834, the MME notifies the associated eNB in the specific area of theinformation for specifying a target UE and the established bearerinformation using a message indicating Connected UE infor Report (UEID,bearer info). This measure is taken to increase the speed of a processprocedure when the UE establishes an RRC Connection/S1 bearer foranother eNB. This procedure may be skipped if higher speed is notrequired. In that case, Step ST1856 that is a Radio Bearer Establishmentprocedure, described below, needs to be performed.

As to the judgment to perform Service Request Procedure (plural RRC) orperform a normal UE triggered Service Request procedure, for example, atarget eNB transmits, in the system information or the like, theinformation for enabling the judgment as to whether its area is an areain which the establishment of a plurality of RRC connections ispermitted, and the UE receives the information to judge which of theprocedures to be performed. The UE may use, in its judgment, UEcapability such as the capability regarding whether a plurality of RRCconnections/S1 bearers can be established with a plurality of eNBs orthe moving speed of the UE.

FIG. 18 is a sequence diagram showing details of a cell additionprocedure. In Step ST1838, the UE that has activated Cell AdditionProcedure (eNB#2) issues a request for RRC connection including theinformation for specifying the established EPS bearer being an additiontarget (transmits RRC connection Request (existing EPS bearer)) to theeNB#2.

In Step ST1839, the eNB#2 that has received RRC connection Request(existing EPS bearer) searches for the information notified in advancefrom the MME in Connected UE info Report (UEID, bearer info) or the liketo confirm whether there is the bearer information of a target UE. Thisprocess has an object to take a measure against a case where RRCconnection Request (existing EPS bearer) is inadvertently receivedbefore the notification of Connected UE info Report (UEID, bearer info)due to, for example, a delay in the process between the MME and theeNBs#1, or a case where Connected UE info Report (UEID, bearer info) isnot transmitted in the first place.

If having succeeded in confirming the bearer information of the targetUE in the judgment above, in Step ST1841, the eNB#2 transmits, to theUE, the information of RRC connection corresponding to the bearer in RRCconnection setup (the configuration of an RAB corresponding to anexisting bearer). The UE that has received RRC connection setup (theconfiguration of an RAB corresponding to an existing bearer) performsthe configuration and, in Step ST1842, transmits RRC connection Setupcomplete to the eNB. In Step ST1843, the eNB#2 that has received RRCconnection Setup complete transmits Connected UE Confirmation (UE ID,existing EPS bearer) to the MME.

If having failed to confirm the bearer information of the target UE inthe judgment above, in Step ST1845, the eNB#2 transmits RRC connectionsetup (provisional) as in the RRC Connection setup procedure in ServiceRequest Procedure (plural RRC). The UE that has received RRC connectionsetup (provisional) performs the configuration and, in Step ST1846,transmits RRC connection Setup complete to the eNB. To confirm theestablishment status of a bearer for a target UE, in Step ST1847, theeNB#2 that has received RRC connection Setup complete transmits theinformation for specifying a UE and the information of EPS bearer ofwhich RRC connection has been requested to the MME, using Connected UEConfirmation (UE ID, existing EPS bearer).

In Step ST1850, the MME, which has received Initial Context SetupComplete or Connected UE Confirmation (UE ID, existing EPS bearer),judges whether to add this connection. For [1], in Step ST1840, thelocation information of the target eNB, a traffic status, or the like istaken into account to judge the addition of the connection. For [2], inStep ST1844, the presence of the existing bearer established isconfirmed and, if the such a bearer is present, the addition of theconnection is further made using criteria for judging similar to thoseof [1].

If it is judged that addition cannot be made in this judgment, in StepST1851, the MME notifies the target eNB of Release Request (UE ID,existing EPS bearer), and the eNB that has received this notificationreleases target RRC connection in Step ST1848. If it is judged thataddition is allowed in this judgment, the MME transmits Initial ContextSetup Request to the target eNB in Step ST1852 and also transmits ModifyBearer Request to a target S-GW in Step ST1853, requesting to theconfiguration of adding an S1 bearer.

The eNB that has received Initial Context Setup Request performs theconfiguration and, in Step ST1859, transmits Initial Context SetupComplete to the MME. The S-GW that has received Modify Bearer Requestperforms the configuration and, in Step ST1854, transmits Modify BearerResponse to the MME. In Steps ST1860 to 1862, the MME that has confirmedthe addition of each bearer notifies an associated eNB of an update ofthe bearer information, using Connected UE info Report (UEID, bearerinfo).

Consequently, the addition of an RRC Connection/S1 bearer is enabled.

FIG. 19(A) shows an example sequence of adding an RRC Connection/S1bearer of an eNB#3 initiated from a UE. The procedure of FIG. 19(A) isobtained by adding an RRC Connection/S1 bearer of the eNB#3 initiatedfrom a UE after the procedure of FIG. 18.

FIG. 19(B) is a sequence diagram showing details of a cell additionprocedure. For the procedure added, the eNB#2 of FIG. 18 may be replacedwith an eNB#3, which will not be described here.

FIG. 20 shows an example sequence of adding an RRC Connection/S1 bearerto a target UE in accordance with the judgment by the eNB. Illustratedhere is an example in which the eNB#1 makes judgment. First, in StepST1815 that is Service Request Procedure (plural RRC), the UE completesthe connection with the eNB#1. In Step ST2001, the UE that is connectedwith the eNB#1 notifies the eNB#1 of neighbor cell information inMeasurement Report as usual. The UE may add and notify not only thenormal quality information but also the UE location information of.

In Step ST2002, the eNB that has received Measurement Report judgeswhether to add a target eNB from the received quality information of aneighbor cell or the received UE location information. Although thisjudgment may be similar to the existing judgment regarding handover, itis desirable to take into account the establishment of a plurality ofconnections.

In this example sequence, the addition of an eNB#2 is judged in StepST2002. In Step ST2003, the eNB#1 that has judged the addition requeststhe UE to add the eNB#2 in RRC Connection add Request (eNB 2). The UEthat has received RRC Connection add Request (eNB 2) performs StepST1637 that is Cell Addition Procedure (addition of eNB#2) describedwith reference to FIG. 18 to establish the connection with the eNB#2.

After that, the addition of the eNB#3 is judged in Step ST2005. Afterthat, a process similar to the addition of the eNB#2 is performed. Thisaddition may be judged by the eNB#2 or may be performed any one theeNBs. The judgment by any one of the eNBs needs the process of handingover a judgment authorization between eNBs using, for example, an X2interface. When the judgment is performed by both of the eNBs, the UEdiscards the same request for addition.

FIG. 21 shows an example sequence of adding an RRC Connection/S1 bearerto a target UE in accordance with the judgment by the MME. First, inStep ST1815 that is Service Request Procedure (plural RRC), the UEcompletes the connection with the eNB#1. Notifying each eNB of ConnectedUE info Report (UEID, bearer info) may be omitted here. In Step ST2101,the UE that is connected with the eNB#1 notifies the eNB#1 of neighborcell information in Measurement Report as usual. Here, not only thenormal quality information but also the UE location information may beadded to be notified. In Step ST2102, the eNB#1 that has receivedMeasurement Report notifies the MME of the received information inConnection Quality Report (UEID, Quality (own cell, other cell),Location).

In Step ST2103, the MME that has received Connection Quality Report(UEID, Quality (own cell, other cell), Location) judges whether to add atarget eNB from the received quality information of a neighbor cell andthe received UE location information. This example sequence shows thecase where the addition of the eNB#2 is judged in Step ST2103.

In Step ST2105, the MME that has judged the addition of the eNB#2notifies the eNB#2 of the existing bearer in Connected UE info Report(UEID, bearer info). If notification is made in Service RequestProcedure (plural RRC), the transmission of this message is notrequired.

The MME that has judged the addition of the eNB#2 notifies the eNB#1 ofa request to add the eNB#2 in Connection add Request (eNB 2) in StepST2106, and the eNB#1 notifies the UE of a request to add the eNB#2 inRRC Connection add Request (eNB 2) in Step ST2107. The UE that hasreceived RRC Connection add Request (eNB 2) transmits RRC connectionRequest (existing EPS bearer) to the eNB#2 in Step ST2108, and the eNB#2that has received the request transmits RRC connection setup (theconfiguration of a RAB corresponding to an existing bearer) to the UE inStep ST2109. The UE that has completed the configuration transmits RRCconnection Setup complete to the eNB#2 in Step ST2110, and the eNB#2that has received RRC connection Setup complete transmits Connected UEConfirmation (UE ID, existing EPS bearer) to the MME in Step ST2111.

Hereinafter, the configuration of a bearer is changed using Step ST2112that is Initial Context Setup Request, Step ST2113 that is Modify BearerRequest, Step ST2114 that is Modify Bearer Response, and Step ST2115that is Initial Context Setup Complete among the eNB#2, the MME, and theS-GW, completing the addition of an RRC Connection/S1 bearer. Afterthat, Connected UE info Report (UEID, bearer info) may be notified eacheNB.

Hereinafter, the eNB#3 is added in the same manner as with the eNB#2.

Consequently, the RRC Connection/S1 bearer initiated from the MME can beadded.

FIG. 22 shows an example sequence of releasing the RRC Connection/S1bearer of the eNB#1 initiated from the UE. The UE first completes theconnection with the eNB#1 in Step ST1815 that is Service RequestProcedure (plural RRC), and then, adds the eNB#2 in Step ST1637 that isCell Addition Procedure (addition of eNB#2).

The UE that has established the bearer detects and monitors anotherneighbor cell as in a normal communication operation. Based on thedetection and monitoring results, the UE judges the release of a targeteNB in Step ST2201. As the method for judgment, for example, the UEmakes judgment based on whether the quality of a reference signal of amonitoring cell falls below a set threshold with respect to the currentlevel of a cell or when the distance, which has been calculated betweenthe location information measured by the UE and the location informationof the eNB obtained in advance by any method, falls outside a setthreshold.

If it is judged that release is required in this judgment for release,in Step ST2202, the UE transmits a release request (RRC Release Request(eNB#1)) to the eNB (here, eNB#2) having a good communicationenvironment for connection. The eNB#2, which has received the releaserequest, requests the MME to release the bearer in UE Context ReleaseRequest (eNB#1) in Step ST2204. The MME, which has received UE ContextRelease Request (eNB#1), judges for connection release in Step ST2205.This judgment is performed, for example, as a measure to prevent such asituation that the addition process and the release process are switcheddue to a process delay or the like, and thus, all the bearers arereleased, or to reduce an excessive volume of traffic of the remainingbearers.

If the MME judges that release is not allowed in the connection releasejudgment, the MME notifies the eNB#2 that release is not allowed in UEContext Release Response (reject) in Step ST2206. If the MME judges thatrelease is allowed in the connection release judgment, the MME requeststhe eNB#1 to release the bearer in UE Context Release Command in StepST2209, and the eNB#1 that has completed the release notifies UE ContextRelease Complete in Step ST2211. On this occasion, in Step ST2210, theeNB#1 may transmit RRC Connection Release to the UE. In Step ST2207, theMME requests the S-GW to release a target bearer in Modify BearerRequest (release). After the completion of the configuration, in StepST2208, the S-GW transmits Modify Bearer Response. The MME that hasconfirmed the release of the bearer notifies each eNB of the update ofthe bearer in Connected UE info Report (UEID, bearer info) in StepsST2212 to 2214.

Consequently, the UE-initiated RRC Connection/S1 bearer can be released.

FIG. 23 shows an example sequence of releasing the RRC Connection/S1bearer of the eNB initiated by itself. As in FIG. 20, the UE firstcompletes the connection with the eNB#1 in Step ST1815 that is ServiceRequest Procedure (plural RRC), and adds the eNB#2 in Step ST1637 thatis Cell Addition Procedure (addition of eNB#2). In Step ST2301, the UEthat is connected with the eNB#1 and the eNB#2 notifies the eNB#1 (andeNB#2) of the neighbor cell information in Measurement Report as usual.Here, not only the normal quality information but also the UE locationinformation may be added to be notified.

In Step ST2302, the eNB that has received Measurement Report judgeswhether to release its link in accordance with the received qualityinformation of a neighbor cell, the UE location information, and theuplink quality information (such as the quality of a reception signal,the number of L2 retransmissions, and an angle of arrival) of a targetUE measured by the eNB.

If it is judged that release is necessary in the judgment for release,in Step ST2304, the eNB#1 requests the MME to release the bearer in UEContext Release Request. The subsequent procedures are similar to RB/S1Release Procedure 2 (release of eNB#1) of FIG. 20.

FIG. 24 shows an example sequence of releasing the RRC Connection/S1bearer of another eNB, which is initiated by the eNB. As in FIG. 20, theUE first completes the connection with the eNB#1 in Step ST1815 that isService Request Procedure (plural RRC), and then adds the eNB#2 in StepST1637 that is Cell Addition Procedure (addition of eNB#2). In StepST2401, the UE that is connected with the eNB#1 and the eNB#2 notifiesthe eNB#2 (and the eNB#1) of the neighbor cell information inMeasurement Report as usual. Here, not only the normal qualityinformation but also the UE location information may be added to benotified.

In Step ST2402, the eNB#2 that has received Measurement Report judgeswhether to release another eNB (here, eNB#1) in accordance with thereceived quality information of a neighbor cell and the UE locationinformation.

If it is judged that release is necessary in the judgment for release,Step ST2203 that is RB/S1 Release Procedure 2 (release of eNB#1) of FIG.22 is activated to release the bearer.

FIG. 25 shows an example sequence of releasing the RRC Connection/S1bearer of the eNB initiated from the MME. As in FIG. 20, the UE firstcompletes the connection with the eNB#1 in Step ST1815 that is ServiceRequest Procedure (plural RRC), and then adds the eNB#2 in Step ST1637that is Cell Addition Procedure (addition of eNB#2). In Step ST2501, theUE that is connected with the eNB#1 and the eNB#2 notifies the eNB#2(and eNB#1) of the neighbor cell information in Measurement Report asusual. Here, not only the normal quality information but also the UElocation information may be added to be notified. In Step ST2102, theeNB#2 that has received Measurement Report notifies the MME of thereceived information in Connection Quality Report (UEID, Quality (owncell, another cell), Location).

In Step ST2502, the MME that has received Connection Quality Report(UEID, Quality (own cell, another cell), Location) judges the release ofa target eNB from the received quality information of a neighbor celland the UE location information.

If judging that release is necessary in the judgment for release, inStep ST2504, the MME requests the S-GW to release a target bearer inModify Bearer Request (release). The subsequent procedures are similarto RB/S1 Release Procedure 2 (release of eNB#1) of FIG. 20.

FIG. 26 shows an example sequence of releasing an RRC Connection/S1bearer when time-out of which is detected. As in FIG. 20, the UE firstcompletes the connection with the eNB#1 in Step ST1815 that is ServiceRequest Procedure (plural RRC), and then, adds the eNB#2 in Step ST1637that is Cell Addition Procedure (addition of eNB#2). After that, if theeNB has not performed data transmission in the radio section of a targetUE for a long period and the eNB#1 detects data time-out (expiration ofdata monitoring timer) in Step ST2602, the procedure of Step ST2603 thatis RB/S1 Release Procedure 1 (release of eNB#1) of FIG. 26 is performed,releasing a target bearer. Also for the UE, a target bearer is releasedin the case where the UE detects data time-out of the eNB#1 (expirationof data monitoring timer) is detected in Step ST2601.

FIG. 27(A) shows an example sequence of data transmission in the casewhere a plurality of RRC connections/S1 bearers are configured. In thisexample, an RRC Connection/S1 bearer has been configured between the UEand each of the eNB#1, the eNB#2, and the eNB#3. Here, downlink datatransmission and uplink data transmission are described separately.Uplink and downlink are not relevant to each other though downlink isdescribed first. Uplink and downlink data transmissions are bothperformed constantly.

The downlink data transmission is described first. In Steps ST2703 to2705, the UE that is connected the eNB#1, the eNB#2, and the eNB#3notifies the eNB#1, the eNB#2, and the eNB#3 of the neighbor cellinformation in Measurement Report as usual. The UE may notify any one ofthe eNBs. Not only the normal quality information but also the UElocation information may be added to be notified.

The following three will be disclosed as specific examples of notifyingany one of the eNBs.

(1) All the measurement results of the eNBs are notified any one of theeNBs.

(2) Although measurement is performed in accordance with the measurementconfiguration of each eNB, reporting is performed to only any of theeNBs in accordance with the configuration.

(3) Measurement is performed in accordance with the measurementconfiguration of any one of the eNBs, and reporting is performed to onlythis one eNB in accordance with the configuration.

In every example, the UE notifies only one eNB, simplifying control toreduce power consumption as a result of reduced transmission time. In(2), further reduced number of transmissions, further simplifiedcontrol, and further reduced power consumption can be achieved becausean event for a measurement report is limited to the measurementconfiguration of any one eNB. In (3), further reduced measurementprocesses, further simplified control, and further reduced powerconsumption can be achieved because measurements are merely performed inaccordance with the configuration of any one eNB.

In Step ST2706, subsequently, a downlink traffic control procedure (DLTraffic Control Procedure) is performed. Subsequent to this, in StepST2715, an uplink traffic control procedure (UL Traffic ControlProcedure) is performed.

FIG. 27(B) is a sequence diagram showing details of the downlink trafficcontrol procedure. In Steps ST2707 to 2709, each eNB that has receivedMeasurement Report notifies the MME of the information in ConnectionQuality Report (UEID, Quality, Location).

The MME that has received Connection Quality Report (UEID, Quality,Location) calculates a ratio of the quality of each link from thereceived quality information of a neighbor cell and the received UElocation information. The MME determines, in Step ST2710, the finalpacket distribution ratio to each eNB in consideration of the ratio ofquality and the traffic situation of each cell, and in Step ST2711,notifies the S-GW of the ratio in Packet DL TX Ratio IND (UEID,Connection1, Connection2, Connection3). The S-GW distributes thereceived packets to each eNB in accordance with the ratio (Steps ST2712to 2714). Here, the packets received by the S-GW are not, for example,separated or combined, and the received packets and the packetstransmitted to each eNB have one-to-one correspondence. The distributionratio is determined constantly in accordance with an update of thequality of each link and traffic data.

Uplink data transmission will now be described.

FIG. 27(C) is a sequence diagram showing details of the uplink trafficcontrol procedure. The UE (AS) that is connected with the eNB#1, theeNB#2, and the eNB#3 measures the quality of the links of the eNB#1, theeNB#2, and the eNB#3 as usual in Step ST2716, notifies the NAS of the UEof the information in Step ST2717, and then calculates the ratio of thequality of each link in Step ST2718. Then, the NAS notifies the AS ofthe ratio in Step ST2719 and distributes the transmission packets to thelink of each eNB in Steps ST2720 and 2721 for transmission. The UEnotifies the amount of transmission data for each eNB in a buffer statusreport (BSR) for each eNB, and performs transmission in accordance withthe scheduling performed by each eNB using the BSR. The distributionratio is performed constantly in accordance with an update of thequality of each link.

All or part of the example sequences of the figures described above maybe applied.

The first embodiment allows a plurality of RRC Connections/S1 bearers tobe configured for one connection, enabling a change of a cell duringcommunication through addition/release of the RRC Connection/S1 bearer.This eliminates the HO procedure as described in Chapter 10.1.2 ofNon-Patent Document 1 (TS36.300), enabling an appropriate cell changealso in the case where the UE moves at some speed in an area where aplurality of small cells are concentrated. In addition, U-plane controlis not required, reducing a load on a network.

Second Embodiment

As described in the first embodiment, an increase in communicationcapacity is required as a system. Downsizing cells to increase spectralefficiency is studied to increase communication capacity. The firstembodiment has disclosed the method of enabling an appropriate cellchange even in a situation where a plurality of small cells, which havebeen downsized, are concentrated.

However, the method disclosed in the first embodiment requires thecontrol process for establishing RRC connection with a plurality of eNBs(cells), causing signaling and a control delay.

The second embodiment therefore discloses the method of performingcommunication using a plurality of eNBs (cells) without establishing RRCconnection with the plurality of eNBs (cells).

3GPP proposes C/U plane split and multi-stream as the method ofperforming communication using a plurality of cells without establishinga plurality of RRC connections (see Non-Patent Document 12 (RWS-120010)and Non-Patent Document 13 (RWS-120006)). Unlike the method ofestablishing RRC connection and a U-plane side bearer using one eNB(cell), which is performed in a conventional communication system, thearchitecture including an MME or an S-GW, the method of establishing abearer, and the like are required to perform communication using aplurality of eNBs (cells) without establishing RRC connection with theplurality of eNBs (cells). There is, however, no disclosure about thearchitecture including an MME or an S-GW, the method of establishing abearer, or the like.

Disclosed here is a method of performing communication using a pluralityof eNBs (cells) without establishing RRC connection with the pluralityof eNBs (cells).

C-plane connection is established using one eNB (cell) for onecommunication, and U-plane connection is established using a pluralityof eNBs (cells). Hereinafter, the eNB (cell) that establishes (shouldestablish or has established) C-plane connection may be referred to as aC-plane establishing eNB (cell), and the eNB (cell) that establishes(should establish or has established) U-plane connection may be referredto as a U-plane establishing eNB (cell). The eNB (cell) that establishesonly U-plane connection may be referred to as a U-plane onlyestablishing eNB (cell).

RRC connection is established as C-plane connection, and a bearer isestablished as U-plane connection. The bearer may be a data radio bearer(DRB)/S1 bearer. The DRB is a radio bearer for user data.

The eNB whose bearer alone is established has at least a functionrelated to bearer control.

An example of the function related to bearer control is the function ofestablishing/controlling/releasing E-RAB being the bearer between theS-GW and the UE. Specific examples thereof include the function ofestablishing, configuring, maintaining, and releasing point to pointradio bearers and the E-RAB service management function.

As the method of deploying cells, a coverage cell for providingfundamental coverage and a capacity cell (capacity booster cell) forincreasing communication capacity are studied (see Non-Patent Document14 (TR36.927)). The eNB (cell) that establishes C-plane connection maybe a coverage cell, and the eNB (cell) that establishes only U-planeconnection may be a capacity cell.

The eNB (cell) that establishes C-plane connection may be a macro eNB(cell), and the eNB (cell) that establishes only U-plane connection maybe a small eNB (cell).

The macro eNB is an eNB that configures a macro cell with a relativelywide coverage area. The macro eNB may be a wide area base station (seeNon-Patent Document 15 (TS36.141)).

The small eNB is an eNB that configures a small cell with a relativelynarrow coverage area. The small eNB may be a low power node, local areanode, hotspot, or the like. Alternatively, the small eNB may be a picoeNB (cell), femto eNB (cell), HeNB, RRH, RRM, or RN. Stillalternatively, the small eNB may be a local area base station or homebase station (see Non-Patent Document 15 (TS36.141)).

The eNB (cell) that establishes U-plane connection may be merelyreferred to as a node because it needs not to have all the functions ofthe eNB or cell.

If the eNB that establishes only U-plane connection is an RN, the DeNBmay be a C-plane establishing eNB. The method disclosed in a secondmodification of the second embodiment, described below, may be applied.A backhaul link established between the DeNB and the RN may be used asthe interface between a C-plane establishing eNB and a U-planeestablishing eNB. In this case, a configuration may be made such thatthe frequency layer of the link between the DeNB and the UE differs fromthe frequency layer of the link between the RN and the UE. For the RN,the interface between the C-plane establishing eNB and the U-planeestablishing eNB is a radio, enabling a number of U-plane establishingeNBs to be installed flexibly.

FIG. 28 shows the architecture of an EPS according to the secondembodiment. 2801, 2802, 2803, 2804, 2805, and 2806 denote P-GW, S-GW,MME, C-eNB, U-eNB, and UE, respectively. The eNB that establishesC-plane connection is denoted as a C-eNB, and the eNB that establishesonly U-plane connection is established is denoted as a U-eNB. The C-eNBmay establish C-plane connection as well as U-plane connection.

2807 denotes an interface (S5) between the P-GW and the S-GW; 2808, aninterface (S11) between the MME and the S-GW; 2809 and 2815, aninterface (S1-MME) between the MME and the eNB (C-eNB, U-eNB); 2813 and2814, an interface (S1-U) between the S-GW and the eNB (C-eNB, U-eNB);2810 and 2811, an interface (Uu) between the eNB (C-eNB, U-eNB) and theUE; and 2812, an interface between the eNBs. The interface 2812 may beX2 or a new interface may be provided. As in FIG. 14, the solid linerepresents an interface that supports user traffic (U-plane), and thedashed line represents an interface that supports signaling (C-plane).

A plurality of eNBs are used for one communication as in FIG. 15disclosed in the first embodiment. In this embodiment, however, RRCconnection is established by one eNB. In other words, C-plane connectionis established using one eNB, and U-plane connection is establishedusing a plurality of eNBs. In the example of the figure, one eNB thatestablishes C-plane connection is the C-eNB, and a plurality of eNBsthat establish U-plane connection are the C-eNB and U-eNB.

In this embodiment, RRC connection is established using the Uu (2810)interface between the C-eNB (2804) and the UE (2806) being acommunication target. That is, with reference to the figure, C-planeconnection indicated by the dashed line is established between the C-eNB(2804) and the UE (2806). Meanwhile, only the communication ofU-plane-side data (user data) is performed using the Uu (2811) interfacebetween the U-eNB (2805) and the UE (2806) being a communication target.That is, only the U-plane connection indicated by the solid line isestablished between the U-eNB (2805) and the UE (2806). U-planeconnection may be established between the C-eNB (2804) and the UE (2806)as in conventional cases.

Although the interface 2811 for U-plane connection between the U-eNB(2805) and the UE (2806) is Uu here, not Uu but a new interface may beprovided which has only a U-plane connection function.

In this embodiment, for the UE (2806) being a communication target, theuser data is communicated between the U-eNB (2805) and the S-GW (2802)using the interface (S1-U) 2813. For the UE (2806) being a communicationtarget, signaling is communicated between the U-eNB (2805) and the MME(2803) using the interface (S1-MME) 2815. As described below, however,the signaling for the UE (2806) being a communication target is limited.This signaling may be signaling required for performing at least bearercontrol by the U-eNB (2805).

Here, the UE (2806) corresponds to a mobile station; the C-eNB (2804), afirst base station; the U-eNB (2805), a second base station; and the MME(2803) and the S-GW (2802), a gateway station. For C-plane signals, theRRC connection between the UE (2806) and the C-eNB (2804) corresponds toa first radio communication connection. Similarly, for C-plane signals,the S1-MME signaling connection (2809) between the MME (2803) and theC-eNB (2804) corresponds to a first communication connection, and theS1-MME signaling connection (2815) between the MME (2803) and the U-eNB(2805) corresponds to a second communication connection. For U-planesignals, the radio bearer between the UE (2806) and the C-eNB (2804)corresponds to a first radio communication connection, and the radiobearer between the UE (2806) and the U-eNB (2805) corresponds to asecond radio communication connection. Similarly, for U-plane signals,the S1 bearer (2814) between the S-GW (2802) and the C-eNB (2804)corresponds to a first communication connection, and the S1 bearer(2813) between the S-GW (1506) and the U-eNB (2805) corresponds to asecond communication connection.

One communication is performed between the mobile station and thegateway station by establishing the first communication connectionbetween the gateway station and the first base station, the secondcommunication connection between the gateway station and the second basestation, the first radio communication connection between the first basestation and the mobile station, and the second radio communicationconnection between the second base station and the mobile station asdescribed above. A cell change is accordingly enabled through additionor release of the communication connection or the radio communicationconnection.

The U-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and a second path including the secondcommunication connection and the second radio communication connection.The C-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and a second path including the secondcommunication connection and the second radio communication connection.

FIG. 29 shows the protocol stack of the eNB according to the secondembodiment. 2901 denotes a C-eNB, which is connected to the S1-MMEinterface as C-plane and is connected to the S1-U interface as U-plane.A portion 2902 surrounded by a dashed line is a protocol for C-planeconnection, and a portion 2903 surrounded by a dashed line is a protocolfor U-plane connection. In the C-eNB, 2904 denotes an RRC protocol;2907, a PDCP protocol; 2908, an RLC protocol; 2912, a MAC protocol; and2911, a PHY protocol. The MAC protocol 2912 has a multiplexing(MPX)/scheduling function 2909 and a HARQ function 2910. These protocolsalso function for C-plane and U-plane. For C-plane, the protocol haspaging, system information (SI), and a signaling function of the controlinformation by a signaling radio bearer (SRB) being a radio bearer forsignaling (2905). For U-plane, the protocol has a user data transmissionfunction by a data radio bearer (DRB) being a radio bearer for user dataDRB (2906).

2913 denotes a U-eNB, which is connected to the S1-MME interface asC-plane and is connected to the S1-U interface as U-plane.

First, the protocol for the UE that establishes C-plane connection forthe U-eNB will be described. A portion 2914 surrounded by a dashed lineis the protocol for C-plane connection, and a portion 2915 surrounded bya dashed line is the protocol for U-plane connection. In U-eNB, 2917denotes an RRC protocol; 2920, a PDCP protocol; 2921, an RLC protocol;2925, a MAC protocol; and 2924, a PHY protocol. The MAC protocol 2925has a multiplexing (MPX)/scheduling function 2922 and a HARQ function2923. These protocols also function for C-plane and U-plane.

Next, the protocol for the UE that establishes only U-plane connectionwill be described. The protocol 2914 for C-plane connection is notconfigured, which, however, has at least a function 2916 relating tobearer control. The function 2916 may be possessed as an RRC function.The PDCP protocol 2920, RLC protocol 2921, MAC protocol 2922, and PHYprotocol 2924 accordingly have only the function for U-plane, that is,have only the function for establishing a bearer.

In configuring an eNB dedicated for establishing U-plane, the protocol2914 for establishing C-plane connection needs not to be included in theU-eNB 2913, leading to a simplified configuration.

A method of establishing a bearer using a plurality of eNBs (cells) willnow be disclosed.

In this embodiment, the MME selects an eNB with which a DRB/S1 bearershould be established for the UE being a communication target.

For example, the quality information or location information notified inthe measurement report of a UE, which has been disclosed in the firstembodiment, may be used as criteria for selection.

The following eleven are specific examples of criteria for selection.

(1) Quality information on communication between a UE and a cell.

(2) UE location information.

(3) Path loss between a UE and a cell.

(4) Arrival information of a reception wave from a UE in a cell.

(5) Speed or speed class of a UE.

(6) Traveling direction of a UE.

(7) Delivery confirmation result at Uu between a UE and a cell.

(8) Load status of a cell.

(9) UE capability information.

(10) UE type information.

(11) Combination of (1) to (10).

As to (1), specific examples of the quality information on communicationinclude the RSRP and RSRQ measured by the UE. The quality information oncommunication may be uplink communication quality measured by a cell. Asto (2), the UE with a global positioning system (GPS) or the UEconnectable with a GPS can obtain the UE location information throughmeasurement. This UE location information may be used. In anothermethod, a location service (LCS) may be used. A network-side node mayobtain the location information of a target UE from the LCS server. Asto (3), if the UE can measure a path loss from the reception power fromthe cell and the cell transmission power notified from the cell, thispath loss information may be used. The specific example (4) may be usedif the cell can measure an angle of arrival (AoA) of a reception wavefrom a UE. The specific example (5) may be measured by the UE with a GPSor the UE connectable with a GPS, using the GPS. Or, the speeds may beclassified into predetermined speed classes and represented as speedclass. In another method, a speed class may be derived from the numberof HOs or the number of changes of connection of a macro cell in apredetermined period of time, or the number of changes of connection ofa small cell in a predetermined period of time. The derivation may beperformed by a network-side node, not by a UE. The specific example (6)may be measured by the UE with a GPS or the UE connectable with a GPS,using the GPS. In another method, the travelling direction of a UE maybe derived from the number of HOs or the number of changes of connectionof a macro cell in a predetermined period of time or the number ofchanges of connection of a small cell. The derivation may be performedby a network-side node, not by a UE. The network-side node may recognizethe position of a macro cell or a small cell to measure the travelingdirection of a UE depending on an order in which the cell to which theUE connects has been changed. As to (7), the confirmation result of datadelivery performed between the UE and the cell may be used. Specificexamples thereof include HARQ and ARQ. The eNB (cell) can obtain thedelivery confirmation result at Uu between the UE and the own cell. Asto (8), each cell may notify the MME or a neighbor cell of theinformation indicative of the load status of the own cell. The cell loadstatus may be a cell traffic status. As to (9), the capabilityinformation of a UE is, for example, the information indicative of thenumber of eNBs that can establish a DRB/S1 bearer (in application to thefirst embodiment, the information indicative of the number of eNBs thatcan establish an RRC connection/S1 bearer). Or, the capabilityinformation of a UE may be the UE capability information specified inspecifications. As to (10), examples of the UE type information includethe information indicative of whether the UE is a terminal for a machinetype communication (MTC) or a normal UE.

Disclosed below is a method of recognizing, by an MME, the criteria inselecting an eNB that should establish a DRB/S1 bearer with the UE.

In the use of the information measured by the UE as criteria (alsoreferred to as UP supported information), the information is notifiedfrom the UE to a C-plane establishing eNB. RRC signaling may be used inthe notification.

The following three are described as specific examples of the triggerfor notification.

(1) Instruction from a C-plane establishing eNB.

(2) Periodically.

(3) Occurrence of an event.

As to (2), for example, notification is made in accordance with apredetermined time period. This period may be notified in advance fromthe C-plane establishing eNB to the UE or may be determined in advancein specifications or the like as a system.

As to (3), for example, notification may be made in the occurrence of anevent in accordance with predetermined criteria, for example,notification is made when a measured value exceeds a predeterminedthreshold.

Specific examples of the UE supported information include

(1) Information measured by a UE, and

(2) Cell identifier.

(1) is, for example, the information obtained by a UE throughmeasurement among the above-mentioned criteria for selection. (2) may benotified in the case where it is necessary to identify to which cell theinformation relates.

The conventional measurement event may be used in the method ofnotifying UE supported information. The following two are specificexamples of the information notified in a measurement report.

(1) Quality information on communication between a UE and a cell, suchas RSRP or RSRQ.

(2) Cell identifier.

In addition, the UE supported information may be included in ameasurement report. The UE notifies the C-plane establishing eNB of theinformation described above in the measurement report.

The C-plane establishing eNB that has received the information notifiesthe MME of the information. S1 signaling may be used in thenotification. In this case, the information for recognizing a UE fromwhich UE information is transmitted may be included. The information maybe a UE identifier (UE-ID) identifiable by the MME or may be a mobilesubscriber identity identifiable by the MME. The information may be a UEidentifier used in the MME, mobile subscriber identity, or theidentifier of the own cell (C-plane establishing eNB (cell) for the UE)and the UE identifier used in the own cell (C-plane establishing eNB(cell)).

The MME can use the UE supported information received from the C-planeestablishing eNB to select an eNB with which a DRB/S1 should beestablished.

In the use of the information measured or obtained by a network-sidenode as criteria, each node notifies the MME of the information. Whenthe network-side node is an MME, no notification is required. As in themethod described above, there may be included the information forrecognizing the information of which UE, information with which eNB(cell), and information of which eNB (cell).

This method can be applied to the case in which an eNB selects anothereNB, disclosed in the first embodiment, and can also be applied to thecases in which the C-plane establishing eNB selects a U-planeestablishing eNB in a third modification of the second embodiment to afirst modification of a third embodiment described below. In this case,the C-plane establishing eNB needs not to notify the MME of theinformation.

Alternatively, this method is also applicable to determination of packetallocation (determination of packet transmission allocation) describedbelow, disclosed in the first embodiment. Still alternatively, if thequality information on uplink communication with each U-planeestablishing eNB can be used, the information may be used to determinepacket allocation. The quality information on uplink communication withthe UE is measured by a U-plane establishing eNB. The U-planeestablishing eNB may notify the MME of the information.

To establish an E-RAB, the MME configures the E-RAB of each eNBselected. Specific examples of the E-RAB configuration include an E-RABidentifier (E-RAB ID) and a QoS parameter.

If there is an eNB that has established an E-RAB, the MME modifies theE-RAB configuration for the eNB.

If there is only one EPS bearer, the E-RAB configuration to beconfigured for each eNB may be the same. If there is no change in theEPS bearer, the E-RAB configuration may be the same as the E-RABconfiguration that has been configured for the C-plane establishing eNB.In this case, only the E-RAB identifier may differ. This allows theE-RAB configuration in each eNB to be dedicatedly handled using theidentifier.

The MME notifies each eNB of the information for configuring an E-RABwith the UE being a communication target. The examples of theinformation include the information about the UE being a communicationtarget, the E-RAB configuration configured or modified by the MME. Themodified E-RAB configuration may not be notified the eNB whose E-RABconfiguration has not been changed after the modification of the E-RABby the MME.

Initial context setup request message of S1 may be used as signaling. Ofthe initial context setup request message, only the information relatedto the E-RAB configuration may be notified. The UE context modificationrequest message of S1 may be used to modify the information related tothe UE.

The E-RAB setup request message of S1 may be used to configure an E-RAB.The E-RAB modify request message may be used to modify the configuredE-RAB.

There may be newly provided a list of the correspondence between each ofthe U-plane establishing eNBs and the E-RAB configuration of each of theU-plane establishing eNBs. E-RAB list_U-plane may be provided. The MMEmay notify each U-plane establishing eNB of the list. This allows eachU-plane establishing eNB to recognize the E-RAB configuration of anotherU-plane establishing eNB.

The MME may also notify each U-plane establishing eNB of the informationabout a C-plane establishing eNB. The information may be notifiedtogether with the information for configuring the E-RAB. The informationabout a C-plane establishing eNB may be the identifier or address of theC-plane establishing eNB. This allows each U-plane establishing eNB tonotify the C-plane establishing eNB of the necessary information. Forexample, in such a case where the DRB configuration informationconfigured by each U-plane establishing eNB is notified the UE via aC-plane establishing eNB, described below, the DRB configurationinformation can be notified the C-plane establishing eNB.

Each U-plane establishing eNB uses the E-RAB configuration informationreceived from the MME to perform the process required for establishing aDRB/S1 bearer for the UE being a communication target. Each U-planeestablishing eNB configures a DRB for a radio section. Each U-planeestablishing eNB uses the E-RAB configuration notified from the MMEthrough the RRC function to configure a DRB to be established between aUE being a communication target and itself. Examples of the DRBconfiguration include the configuration of a DRB identifier and theconfiguration of a lower layer. Examples of the lower layer include thePDCP configuration, RLC configuration, MAC configuration, and PHYconfiguration.

Each U-plane establishing eNB that has configured a DRB notifies the UEof the DRB configuration information. The DRB configuration informationmay include the identifier of the own eNB (cell) for identifying the DRBconfiguration information of which U-plane establishing eNB or theidentifier of the UE being a communication target to be notified. EachU-plane establishing eNB may notify the system information of the owneNB (cell). In the case where each U-plane establishing eNB configuresan ePDCCH being an extended downlink control channel for scheduling forthe UE being a communication target, the ePDCCH configurationinformation may be notified together. Alternatively, the informationindicative of a request for establishing U-plane may be notifiedtogether.

Disclosed below are two specific examples in which a U-planeestablishing eNB notifies a UE of the DRB configuration information,system information, the ePDCCH configuration information, and theinformation indicative of a request for establishing U-plane.

(1) Notification is made via a C-plane establishing eNB.

(2) Notification is made via an MME and a C-plane establishing eNB.

The method (1) of making notification via a C-plane establishing eNBwill be disclosed. Each U-plane establishing eNB that has configured aDRB notifies the C-plane establishing eNB of, for example, the DRBconfiguration information. A new interface may be provided or an X2interface may be provided in this notification. A new message may beprovided for notification.

The DRB configuration information or the like may be provided as thetransparent container information. For transparent containerinformation, the C-plane establishing eNB (cell) may notify the UE ofthe container information as it is. The information included in theAS-config message of the U-plane establishing eNB may be listed on thecontainer information. The DRB configuration information and the systeminformation per U-plane establishing eNB may be included inRadioResourceConfigDedicated information of the AS-config message. Theinformation may be a DRB list.

The C-plane establishing eNB (cell) notifies the UE of, for example, DRBconfiguration information of each of all the U-plane establishing eNBs,which establish U-plane between the UE and them.

A list of each U-plane establishing eNB and its DRB configuration (DRBlist_U-plane) may be provided. The C-plane establishing eNB may notifythe UE of the list.

RRC signaling may be used in this notification. A new message may beprovided, or the DRB configuration information of the U-planeestablishing eNB and the system information may be included in anexisting RRC message to be notified. The RRC connection reconfigurationmessage or AS-config message may be used as a specific example of theexisting RRC message. The DRB configuration information and the systeminformation per U-plane establishing eNB may be included in theRadioResourceConfigDedicated information in the RRC connectionreconfiguration message or AS-config message. The information may be aDRB list.

Notification can be made without using an MME in the method (1),reducing an amount of signaling as a system.

The method (2) of making notification via an MME and a C-planeestablishing eNB will be disclosed. Each U-plane establishing eNB thathas configured a DRB notifies the MME of the DRB configurationinformation or the like.

An S1 interface may be used in this notification.

The MME notifies the C-plane establishing eNB of the DRB configurationinformation or the like. A list of each U-plane establishing eNB and itsDRB configuration may be provided. The list may be DRB list_U-plane. AnS1 interface may be used in this notification. A new message may beprovided for notification using an S1 interface.

The C-plane establishing eNB (cell) notifies the UE being acommunication target of the DRB configuration information or the likereceived from the MME. A list of each U-plane establishing eNB and itsDRB configuration may be provided. The list may be DRB list_U-plane. TheC-plane establishing eNB may notify the UE of the list. RRC signalingmay be used in this notification. The method (1) is applicable to thisnotification.

The DRB configuration information or the like may be provided astransparent container information also in (2). For the transparentcontainer information, the MME may notify the C-plane establishing eNBof the container information as it is. Further, the C-plane establishingeNB (cell) may notify the UE of the container information as it is. Theinformation included in the AS-config message of a U-plane establishingeNB may be listed on the container information. TheRadioResourceConfigDedicated information of the AS-conifg message mayinclude the DRB configuration information and the system information perU-plane establishing eNB. The information may be a DRB list.

The method (2) allows the UE to be notified of the DRB configurationinformation even in the case where no interface is provided between theC-plane establishing eNB and the U-plane establishing eNB.

The UE being a communication target can thus recognize the DRBconfiguration information for establishing a DRB with the eNB with whicha U-plane is established. The UE can also recognize the systeminformation for connecting with the eNB with which U-plane isestablished.

The UE being a communication target configures a DRB with each U-planeestablishing eNB and performs the process for connection with eachU-plane establishing eNB (cell).

For successful connection with a U-plane establishing eNB, the UE beinga communication target may notify each U-plane establishing eNB of aconnection complete message. To recognize the identifier of the own UE(the identifier of the UE being a communication target) and a U-planeestablishing eNB with which the UE has completed connection, the messagemay include the identifier of a U-plane establishing eNB (cell) withwhich the UE has completed connection.

Disclosed below are three specific examples of the notification method.

(1) Notifying each U-plane establishing eNB via a C-plane establishingeNB and an MME.

(2) Notifying each U-plane establishing eNB via a C-plane establishingeNB.

(3) Directly notifying a U-plane establishing eNB.

The method (1) will be disclosed. A connection complete message isnotified each U-plane establishing eNB from a UE via a C-planeestablishing eNB and an MME. The UE has established no RRC connectionwith the eNB with which only U-plane is established, and thus cannotdirectly notify the U-plane only establishing eNB of the message throughRRC signaling. Thus, the method of making notification via a C-planeestablishing eNB, disclosed in (1), is effective. The UE may notify aC-plane establishing eNB through RRC signaling. RRC connectionreconfiguration complete may be used as an RRC message.

The C-plane establishing eNB may notify the MME of the message using anS1 interface. An S1 message may be newly provided. The method (1) iseffective also in the case where no X2 interface is provided.

The MME may notify each U-plane establishing eNB of the message using anS1 interface.

The method (2) will be disclosed. The connection complete message isnotified each U-plane establishing eNB from a UE via a C-planeestablishing eNB. The UE may notify the C-plane establishing eNB throughRRC signaling. RRC connection reconfiguration complete may be used as anRRC message.

A new interface may be provided or an X2 interface may be used in thenotification from the C-plane establishing eNB to each U-planeestablishing eNB. In the case of the X2 interface, notification can bemade without any new interface provided.

The method (3) will be disclosed. The connection complete message isnotified each U-plane establishing eNB from the UE. The UE hasestablished no RRC connection with the U-plane only establishing eNB,and thus cannot directly notify the U-plane only establishing eNB of themessage through RRC signaling.

Here, an L1/L2 control message is newly provided for the notification.The U-plane establishing eNB has a protocol of an L1/L2 layer.Therefore, newly providing a signaling message at the L1/L2 layer allowsthe UE to notify the U-plane establishing eNB of the message. Themessage may be provided as MAC function or PHY function in L1/L2 layer.Alternatively, the identifier of the own UE may be notified togetherwith the L1/L2 control message. Still alternatively, the code with theidentifier of the own UE may be listed on the radio resource used forthe L1/L2 control message. Demodulation using the code allows theU-plane establishing eNB (cell) to identify from which UE message istransmitted.

Each U-plane establishing eNB that has received the connection completemessage performs the process of establishing a DRB/S1 bearer with the UEbeing a communication target.

Each U-plane establishing eNB may notify the MME of the messageindicative of the completion of the process or may notify that the DRBconfiguration or the configuration of the modified DRB is completebetween the UE and the U-plane establishing eNB. An Initial contextsetup complete message of S1 may be used in this notification.Alternatively, an E-RAB configuration complete message or E-RABmodification complete message may be notified.

This message may include a UE identifier (UE-ID) of a UE being acommunication target, which is identifiable by an MME. Alternatively,this message may be a mobile subscriber identity identifiable by theMME, or may include the identifier of the own U-plane establishing eNB(cell). The UE identifier identifiable by an MME may be a UE identifierused in the MME. Still alternatively, the message may be the identifierof a C-plane establishing eNB (cell) for the UE and the UE identifierused in the C-plane establishing eNB (cell).

The MME requests the S-GW to configure an S1 bearer for the selectedU-plane establishing eNB. An S11 interface may be used for this request.For example, a modify bearer request message may be used. The messagemay include the identifier of a UE being a communication target, theidentifier of the selected U-plane establishing eNB, and the E-RABconfiguration information of each U-plane establishing eNB. E-RABlist_U-plane, being a list of the correspondence between each of theU-plane establishing eNBs and the E-RAB configuration of each of theU-plane establishing eNBs, may be used. An IP address configured foreach U-plane establishing eNB may be used as the identifier of eachU-plane establishing eNB.

The S-GW configures an S1 bearer for each U-plane establishing eNB thathas been notified. If an S1 bearer has been configured, the S-GWmodifies the S1 bearer.

The S-GW that has configured or modified the S1 bearer notifies the MMEof a message indicative of the completion or modification of theconfiguration of the S1 bearer. An S11 interface may be used in thisnotification. A Modify bearer response message of S11 may be used.

An S1 bearer is thus established between the S-GW and each U-planeestablishing eNB.

Disclosed below is a data transmission method in the case where aplurality of DRBs/S1 bearers have been established using a plurality ofeNBs. The DRBs/S1 bearers have been established using a plurality ofU-plane establishing eNBs, which allows for the application of the datatransmission method disclosed in the first embodiment.

For downlink data transmission, the MME calculates the ratio of thequality of each link. The MME determines the final packet distributionratio for each eNB in consideration of the ratio of the quality and thetraffic status of each cell, and then, notifies the S-GW of the ratio inPacket DL TX Ratio IND. The S-GW distributes the received packets toeach eNB in accordance with the ratio. Here, the packets received by theS-GW are not, for example, separated or combined, and the receivedpackets and the packets transmitted to each eNB have one-to-onecorrespondence. The distribution ratio is determined constantly inaccordance with an update of the quality of each link and the trafficdata. The MME may use the criteria for selection of a U-planeestablishing eNB to calculate the ratio of the quality of each link.

In uplink data transmission, the UE measures the quality of the linkbetween the U-plane establishing eNB and itself to calculate the ratioof the quality of each link. Then, the UE distributes transmissionpackets to the link of each eNB in accordance with the ratio andtransmits the packets. The UE notifies an amount of transmission datafor each eNB in a buffer status report (BSR) for each eNB and performstransmission in accordance with the scheduling performed using the BSRin each eNB. The distribution ratio is constantly determined inaccordance with an update of the quality of each link.

Disclosed below is a method in which a U-plane establishing eNB startstransmitting data to a UE being a communication target.

Each U-plane establishing eNB may start the process of transmitting datato the UE upon receipt of a message indicative of the completion of theconnection with the U-plane establishing eNB from a UE. Upontransmission of a connection complete message to a U-plane establishingeNB, the UE may start the process of receiving data from the U-planeestablishing eNB (cell). This reduces a difference of the timing forstarting the process of transmitting and receiving data between the UEand the U-plane establishing eNB (cell).

Another method will be disclosed. The U-plane establishing eNB receivesdata from the S-GW, and then starts the process of transmitting data tothe UE. The UE detects a U-plane establishing eNB (cell) andsynchronizes therewith, and then, starts the process of receiving fromthe U-plane establishing eNB (cell). Alternatively, after the successfulRA procedure with a U-plane establishing eNB (cell), the UE may startthe process of receiving from the U-plane establishing eNB (cell). Forexample, this method is applicable in the case where there is no messageindicative of the completion of the connection with the U-planeestablishing eNB from the UE. This method needs no explicit trigger forstarting data transmission and reception, and advantageously simplifyingcontrol.

If there is no message indicative of the completion of the connectionwith the U-plane establishing eNB from the UE, before the UE completesthe connection with the U-plane establishing eNB, the S-GWconfigures/modifies the S1 bearer so that downlink data will arrive atthe U-plane establishing eNB in some cases. In such cases, the U-planeestablishing eNB starts the process of transmitting data to the UE afterreceiving the data from the S-GW. The UE has not completed theconnection with the U-plane establishing eNB, and thus fails to receivethe data.

However, the use of retransmission control by the U-plane establishingeNB reduces undeliveries of the data. Increasing the maximum number ofretransmission in advance eliminates almost all the undeliveries of thedata. The method disclosed here accordingly leads to an effect ofsimplifying control with hardly any undelivery of data.

Disclosed below is a method in which a UE transmits/receives U-planedata to/from a U-plane establishing eNB (cell).

The U-plane establishing eNB (cell) maps the scheduling information forthe UE to the PDCCH or ePDCCH being a physical control channel and thennotifies the scheduling information. For the ePDCCH, the U-planeestablishing eNB (cell) notifies the UE of the configuration informationof the ePDCCH in advance. Specific examples of the information includeresource (physical resource block (PRB), sequence) information for use.The ePDCCH may be configured through an RRC function or may beconfigured through an RRC function of the U-plane establishing eNB. TheePDCCH configuration information may be notified a UE being acommunication target via a C-plane establishing eNB (cell) as describedabove or, in another method, may be notified from a U-plane establishingeNB (cell) via a MAC through an RA procedure.

The UE monitors the PDCCH of the U-plane establishing eNB (cell).Alternatively, if scheduling is made using an ePDCCH, the UE may monitorthe ePDCCH. Data scheduling information is obtained upon receipt of thePDCCH or ePDCCH, and data may be received in accordance with thescheduling information. Data is mapped to the PDSCH by each U-planeestablishing eNB (cell) and is then allocated to physical radioresources.

DRX may be configured for a U-plane establishing eNB (cell). The DRX fora U-plane establishing eNB may be configured by an RRC. When configuredby a U-plane establishing eNB, DRX may be the RRC function provided inthe U-plane establishing eNB. The DRX configuration may be performed bya U-plane establishing eNB to be notified the UE via a C-planeestablishing eNB (cell) or may be notified from a U-plane establishingeNB (cell) via a MAC through an RA procedure.

The DRX configuration may be performed by a C-plane establishing eNB(cell) to be notified the UE and each U-plane establishing eNB (cell).

DRX may be activated/deactivated by a MAC, which may be the function ofthe MAC provided in each U-plane establishing eNB.

Semi persistent scheduling (SPS) may be configured for a U-planeestablishing eNB (cell). Time configuration for SPS is performed in RRC.If a U-plane establishing eNB performs time configuration, the timeconfiguration for SPS may be the RRC function provided in the U-planeestablishing eNB. The SPS configuration may be performed by a U-planeestablishing eNB (cell) to be notified a UE via a C-plane establishingeNB (cell), or may be notified from a U-plane establishing eNB (cell)via a MAC through an RA procedure.

The SPS configuration may be performed by a C-plane establishing eNB(cell) to be notified a UE and each U-plane establishing eNB (cell).

Scheduling on the frequency axis of SPS may be performed by a MAC. Thescheduling may be the function of the MAC provided in each U-planeestablishing eNB. The scheduling result on the frequency axis may benotified the UE over the PDCCH or ePDCCH being a physical controlchannel for scheduling.

Data scheduling timing may differ between U-plane establishing eNBs(cells). In other words, the data transmission and reception timing maybe time-divided among U-plane establishing eNBs (cells). The UE with asingle transceiver can support the communications with a plurality ofU-plane establishing eNBs. The DRX configuration may be used such thatthe data scheduling timing differs among a plurality of U-planeestablishing eNBs (cells). Alternatively, the SPS configuration may beused. The DRX configuration or SPS configuration for each U-planeestablishing eNB may be performed by a C-plane establishing eNB, wherethe method of notifying a UE and each U-plane establishing eNB (cell)may be applied.

The method disclosed in a seventh embodiment described below may beapplied. As opposed to the seventh embodiment in which a master eNBperforms a time configuration for each slave eNB, the master eNB may bea C-plane establishing eNB and each slave eNB may correspond to eachU-plane only establishing eNB.

In another method, the data scheduling timing may be configured to fallwithin the same period among U-plane establishing eNBs (cells). Datascheduling and data transmission and reception are performed by all theU-plane establishing eNBs within the same period. For this purpose, theDRX configuration or SPS configuration described above may be used.

Not for all the U-plane establishing eNBs but for a plurality of groupsof U-plane establishing eNBs in which the eNBs are divided, datascheduling timing may be configured to fall within the same period pergroup of U-plane establishing eNBs.

The timing of transmission and reception by a UE is accordingly limitedto the same period determined in advance, reducing the power consumptionof the UE.

FIG. 30 shows an example sequence according to the second embodiment,which is an example sequence of establishing RRC connection using oneeNB and establishing/modifying a DRB/S1 bearer using a plurality ofeNBs. The processes in the P-GW and HSS are omitted here.

The UE being a communication target is in the RRC_Idle state in 3001. InST3002, a service request process is performed among the UE, the MME,and S-GW via a C-eNB with which RRC connection is established. Throughthis process, a radio bearer 1 (3003) is established between the UE andthe C-eNB, and an S1 bearer 1 (3004) is established between the C-eNBand the S-GW. An E-RAB is thus established between the UE and S-GW. Theuse of the established bearers enables the U-plane data (user data) tobe communicated between the UE and the C-eNB (ST3005) and between theC-eNB and the S-GW (ST3006).

In ST3007, the UE notifies the C-eNB being a C-plane establishing eNB ofa measurement report. The report may include the criteria for causingthe MME to select a U-plane establishing eNB.

In ST3008, the C-eNB that has received the measurement report from theUE notifies the MME of the information. For example, if communicationquality information is used as criteria, a communication qualityinformation report message may be newly provided. The message mayinclude the location information of the own UE.

In ST3009, the MME selects U-plane establishing eNBs for the UE being acommunication target. The C-plane establishing eNB may be selected as aU-plane establishing eNB. The criteria received in ST3008 may be used inthe selection.

In ST3010, the MME that has selected U-plane establishing eNBsconfigures an E-RAB that is established for each of the U-planeestablishing eNBs. It is assumed here that the C-plane establishing eNBalso establishes U-plane for the UE being a communication target. TheE-RAB has been established for the C-eNB, and thus, the E-RABconfiguration is modified. For the U-eNB, the E-RAB configuration withthe UE being a communication target is newly performed.

In ST3011 and ST3012, the MME notifies each of the U-plane establishingeNBs of an E-RAB configuration request message or E-RAB modificationrequest message including E-RAB configuration information.

In ST3013, the C-eNB reconfigures a DRB for the UE being a communicationtarget, using the E-RAB configuration modification information receivedfrom the MME.

In ST3014, the U-eNB performs the process required for establishing aDRB/S1 bearer for the UE being a communication target, using the E-RABconfiguration information received from the MME. The U-eNB configures aDRB for a radio section.

In ST3015, the U-eNB that has configured a DRB in ST3014 notifies theC-eNB of, for example, the DRB configuration information of the own eNB.In this example, a U-plane connection configuration message is newlyprovided as a message to be notified.

In ST3016, the C-eNB that has reconfigured a DRB in ST3013 notifies theUE of the DRB configuration information or the like. If having receivedthe DRB configuration information or the like from the U-eNB in ST3015,the C-eNB also notifies the DRB configuration information or the like ofthe U-plane establishing eNB in ST3016. The DRB configurationinformation of each U-plane establishing eNB (cell), the identifier ofeach U-plane establishing eNB (cell), the system information of eachU-plane establishing eNB (cell), and the configuration information ofthe ePDCCH may be notified in association with each other. RRC signalingand RRC message are used in the notification. Here, an RRC connectionreconfiguration message is used. This message may include theinformation indicative of a request for establishing U-plane.

The UE that has received the RRC connection reconfiguration message inST3016 uses the DRB configuration information of the U-planeestablishing eNB included in the message to configure a DRB for eachU-plane establishing eNB in the case where the message includes theinformation indicative of a request for establishing U-plane.

In ST3017, the UE starts the process of connecting with a U-planeestablishing eNB to be newly established.

In ST3018, the U-eNB (cell) is detected and synchronized. The identifierof the U-plane establishing eNB (cell) received in ST3016 may be used.

In ST3019, the UE notifies the U-eNB (cell) of the PRACH. Theinformation about the PRACH in the system information of the U-planeestablishing eNB (cell) received in ST3016 may be used.

In ST3020, the U-eNB (cell) notifies the UE of timing advanced (TA) foruplink timing adjustment. The distance between the C-eNB (cell) and theUE normally differs from the distance between the U-eNB (cell) and theUE, resulting in different propagation time. Thus, TA for uplink timingadjustment of the C-eNB (cell) cannot be used as one for uplink timingadjustment of the U-eNB (cell), requiring the U-eNB (cell) to newlynotify the UE of TA for uplink timing adjustment of the U-eNB (cell).

Through the above-mentioned processes, the UE completes the process ofconnecting with the U-plane establishing eNB.

In ST3021, the UE that has completed the process of connecting with theU-plane establishing eNB notifies the C-plane establishing eNB of aconnection complete message. Here, an RRC connection reconfigurationcomplete message is used.

The C-eNB that has received the connection complete message in ST3021recognizes that the UE has performed the DRB configuration process ofthe own eNB (cell). The C-eNB also recognizes that the UE has completedthe connection with another U-plane establishing eNB.

In ST3022, the C-eNB that has recognized that the UE had completed theconnection with the U-plane establishing eNB notifies the U-eNB that hascompleted the connection with the UE of a connection complete message. AU-plane connection configuration complete message is newly provided as amessage.

The C-eNB performs the process of configuring the modified DRB with theUE being a communication target and, in ST3037, notifies the MME of anE-RAB modification complete message.

The U-eNB that has received the U-plane connection configurationcomplete message in ST3022 performs the process of establishing a DRB/S1bearer with the UE being a communication target and, in ST3023, notifiesthe MME of an E-RAB configuration complete message. A UE context setupcomplete message may be used in this notification.

The MME, which has received the E-RAB configuration complete message andthe E-RAB modification complete message from the U-plane establishingeNBs including the C-eNB in ST3037 and ST3023, can recognize that theDRB/S1 bearer configuration (modification) of each of the U-planeestablishing eNBs is complete.

In ST3024, the MME, which has recognized that the E-RAB configuration ofeach U-plane establishing eNB is complete, notifies the S-GW of amessage requesting to configure or modify the S1 bearer. A modify bearerrequest message is used here.

In ST3025, the S-GW that has received the message requesting toconfigure or modify the S1 bearer configures or modifies the S1 bearerbetween each U-plane establishing eNB and itself in accordance with theinformation included in the message.

In ST3026, the S-GW that has configured or modified the S1 bearernotifies the MME of an S1 bearer configuration or modification completemessage. A modify bearer response message is used here.

Through the processes above, a DRB 3027 is established between the UEand the U-plane establishing eNB, and an S1 bearer 3028 is establishedbetween the U-plane establishing eNB and the S-GW. This enables datacommunications between the UE and the U-eNB and between the U-eNB andthe S-GW.

In ST3029, the UE receives a PDCCH of a U-plane establishing eNB or, ifan ePDCCH is configured, receives the ePDCCH.

In ST3030, the U-plane establishing eNB performs multiplexing andscheduling of the user data for a UE being a communication target and,in ST3031, maps scheduling information to the PDCCH or ePDCCH andtransmits the scheduling information.

In ST3032, user data is transmitted and received between the UE and theU-eNB. The user data is mapped to the PDSCH or PUSCH in accordance withthe scheduling information to be allocated to physical radio resources.

In ST3033, user data is transmitted and received between the U-eNB andthe S-GW.

Through the processes above, a DRB/S1 bearer is established between theUE and S-GW using a plurality of eNBs (C-eNB, U-eNB), enablingtransmission and reception of user data.

Disclosed below is a method of releasing an eNB that establishes onlyU-plane between the S-GW and the UE being a communication target. Inother words, disclosed below is a method of releasing the E-RABestablished between the S-GW and the UE being a communication target forthe eNB to be released, or a method of releasing the DRB/S1 bearerestablished between the S-GW and the UE being a communication target forthe eNB to be released.

In this embodiment, the MME selects an eNB to be released. The criteriaused when the MME selects an eNB with which a DRB/S1 bearer should beestablished for the UE being a communication target may be applied asthe criteria for selection. The MME selects an eNB to be released usingthe criteria. For example, among the U-plane establishing eNBs, when thecommunication quality between the UE being a communication target andthe U-plane establishing eNB (cell) degrades and falls below apredetermined threshold, the eNB may be selected as an eNB to bereleased.

The MME performs the E-RAB configuration for the UE being acommunication target of the U-plane establishing eNBs except for an eNBto be released. The MME notifies each U-plane establishing eNB of theE-RAB configuration.

An E-RAB modification request message of S1 may be used in thisnotification. The modified E-RAB may need not to be notified the eNBwhose E-RAB configuration has not been changed since the modification ofthe E-RAB by the MME.

The MME notifies the eNB to be released of a command to release theE-RAB established between the eNB and the UE being a communicationtarget. S1 signaling may be used in this notification. A UE contextrelease command message of S1 may be used. The E-RAB release commandmessage of S1 may be used in the release of an E-RAB. The releasecommand message may include the configuration information of an E-RAB tobe released and the UE identifier to allow the recognition of a UE whoseE-RAB is to be released.

The U-plane establishing eNB that has received the command to releasethe E-RAB established between the UE being a communication target anditself performs the process of releasing the DRB/S1 bearer establishedbetween the UE being a communication target for the own eNB and itself.

The process of establishing/modifying the E-RAB described above may beapplied as the process related to each U-plane establishing eNB that hasreceived the E-RAB establishment request message or modification requestmessage.

Disclosed below is a method in which a U-plane establishing eNB releasesthe DRB/S1 bearer established between the UE being a communicationtarget and the own eNB.

The U-plane establishing eNB that performs the process of releasing aDRB/S1 bearer notifies the UE of DRB release information. The DRBrelease information may include the identifier of the UE being acommunication target or the information for recognizing a U-planeestablishing eNB whose DRB is to be released, for example, theidentifier of a U-plane establishing eNB (cell). This message mayinclude the information indicative of a U-plane release request.

Disclosed below are two specific examples of notifying a UE of DRBrelease information or the like.

(1) Making notification via a C-plane establishing eNB.

(2) Making notification via an MME and a C-plane establishing eNB.

The method (1) of making notification via a C-plane establishing eNBwill be disclosed. The U-plane establishing eNB that performs theprocess of releasing a DRB/S1 bearer notifies the C-plane establishingeNB of DRB release information or the like. A new interface may beprovided or an X2 interface may be used in this notification. A newmessage may be provided for notification.

The C-plane establishing eNB (cell) notifies the UE being acommunication target of, for example, the DRB release information of aU-plane establishing eNB whose DRB is to be released.

A list may be provided for the UE being a communication target, in whichthe DRB release information of a U-plane establishing eNB to be releasedand each piece DRB configuration information of each U-planeestablishing eNB correspond to each U-plane establishing eNB. The listmay be included in DRB list_U-plane. The C-plane establishing eNB maynotify the UE of the list.

The method of notifying the UE of DRB configuration information or thelike may be applied as this notification method. DRB release informationand the information indicative of a U-plane release request may beincluded.

The method (1), which is not performed via the MME, reduces an amount ofsignaling as a system.

The method (2) of making notification via an MME and a C-planeestablishing eNB will be disclosed.

The U-plane establishing eNB that performs the process of releasing aDRB/S1 bearer notifies the MME of DRB release information or the like.An S1 interface may be used in this notification.

The MME notifies the C-plane establishing eNB of DRB release informationor the like. A list may be provided, which includes the U-planeestablishing eNB whose DRB is to be released and DRB releaseinformation, and each U-plane establishing eNB and its DRBconfiguration. The list may be included in DRB list_U-plane. An S1interface may be used in this notification. A new message may beprovided for notification using an S1 interface.

The C-plane establishing eNB (cell) notifies the UE being acommunication target of the DRB release information or the like receivedfrom the MME. A list may be provided, which includes each U-planeestablishing eNB and its DRB configuration. The list may be included inDRB list_U-plane. The C-plane establishing eNB (cell) may notify the UEof the list.

The method (1) is applicable as this notification method.

The method (2) allows the DRB release information to be notified the UEeven in the case where no interface is provided between the C-planeestablishing eNB and the U-plane establishing eNB.

The UE being a communication target can accordingly recognize therelease of the DRB/S1 bearer established between the U-planeestablishing eNB to be released and itself.

The UE that has received the DRB release information or the likeperforms the process of releasing the DRB configuration for the U-planeestablishing eNB (cell) whose DRB is to be released, and performs theprocess of disconnecting the connection with the U-plane establishingeNB (cell).

For example, as the process of disconnecting the connection, the processfor synchronization with the U-plane establishing eNB is ended, ormonitoring of the PDCCH or ePDCCH for scheduling from the U-planeestablishing eNB is ended.

The UE, which has performed the process of releasing the DRB between theU-plane establishing eNB and itself and has disconnected the connection,may notify the U-plane establishing eNB of a disconnection completemessage. This message may include the UE identifier (UE-ID),identifiable by the MME, of the UE being a communication target.Alternatively, the message may be a mobile subscriber identityidentifiable by the MME. Still alternatively, the message may includethe identifier of the own U-plane establishing eNB (cell). The UEidentifier identifiable by the MME may be the UE identifier used in theMME. Alternatively, the UE identifier may be the identifier of a C-planeestablishing eNB (cell) for the UE and the UE identifier used in theC-plane establishing eNB (cell).

Disclosed below are three specific examples of the notification method.

(1) Notifying each U-plane establishing eNB to be released via a C-planeestablishing eNB and an MME.

(2) Notifying each U-plane establishing eNB to be released via a C-planeestablishing eNB.

(3) Directly notifying each U-plane establishing eNB to be released.

The method of notifying each U-plane establishing eNB of a connectioncomplete message described above may be applied as these methods.

Each U-plane establishing eNB that has received the disconnectioncomplete message performs the process of releasing the DRB/S1 bearerestablished between the UE being a communication target and itself.

The U-plane establishing eNB that has performed the process of releasingthe DRB/S1 bearer may notify the MME of the release completion. TheU-plane establishing eNB may notify that the release of the DRBestablished between the UE and the U-plane establishing eNB is complete.A UE context release complete message of S1 may be used in thisnotification.

The MME requests the S-GW to release the S1 bearer for the U-planeestablishing eNB to be released. An S11 interface may be used to notifythis request. For example, a modify bearer request message may be used.The request message may include the identifier of the UE being acommunication target, the identifier of the U-plane establishing eNB tobe released, and the E-RAB configuration information of the U-planeestablishing eNB to be released. E-RAB list_U-plane may be used, whichis a list of the correspondence between each of the U-plane establishingeNBs and the E-RAB configuration of each of the U-plane establishingeNBs. The IP address configured for each U-plane establishing eNB may beused as the identifier of each U-plane establishing eNB.

The S-GW releases the notified S1 bearer established between the UEbeing a communication target for the U-plane establishing eNB to bereleased and itself.

The S-GW that has released the S1 bearer notifies the MME of an S1bearer release complete message. An S11 interface may be used in thisnotification. The modify bearer response message of S11 may be used.

The DRB/S1 bearer established between the S-GW and the UE being acommunication target is accordingly released using the U-planeestablishing eNB to be released.

The data transmission method disclosed in the first embodiment may beapplied as the data transmission method, using a plurality of U-planeestablishing eNBs whose DRB/S1 bearer is established between a target UEand themselves except for the released eNB.

FIG. 31 shows an example sequence of releasing the U-plane establishingeNB according to the second embodiment. The sequence shown in FIG. 31 issimilar to the sequence shown in FIG. 30, and thus, the same steps willbe denoted by the same step numbers and common description will beomitted.

In ST3101, the MME that has received a communication quality reportmessage from the C-eNB in ST3008 determines to release one or aplurality of U-plane establishing eNBs among the U-plane establishingeNBs whose U-plane has been established. The selection of anotherU-plane establishing eNB may be performed together.

In ST3010, the MME that has determined a U-plane establishing eNBs to bereleased in ST3101 configures the E-RAB of each of the U-planeestablishing eNBs except for the U-plane establishing eNB to bereleased. In this case, a newly selected U-plane establishing eNB may beincluded. Here, the U-plane establishing eNB to be released is a U-eNB,and the U-plane establishing eNBs except for the U-plane establishingeNB to be released are C-eNBs.

The MME that has configured the E-RAB of each of the U-planeestablishing eNBs notifies the C-eNB of an E-RAB modification requestmessage in ST3011, as described with reference to FIG. 30. The C-eNBthat has received the request message reconfigures a DRB for the UEbeing a communication target.

Meanwhile, in ST3102, the MME that has determined a U-plane establishingeNB to be released in ST3101 notifies the U-plane establishing eNB to bereleased of an E-RAB release command.

In ST3103, the U-eNB that has received the E-RAB release command inST3102 performs the process of releasing a DRB/S1 bearer. The process ofreleasing a DRB is performed for a radio section.

In ST3104, the U-eNB that has performed the process of releasing aDRB/S1 bearer in ST3103 notifies the C-eNB of the DRB configurationrelease information. A U-plane connection reconfiguration message isnewly provided as a message to be notified.

In ST3105, the C-eNB that has received the DRB release information fromthe U-eNB in ST3104 notifies the UE of the DRB configurationinformation.

If the C-eNB reconfigures a DRB, a DRB configuration information on thereconfiguration may be included in the DRB configuration information tobe notified. The DRB release information of the U-plane establishing eNB(cell) to be released, the DRB configuration information of the U-planeestablishing eNB (cell) to be configured/modified, the identifier ofeach U-plane establishing eNB (cell), and the system information of eachU-plane establishing eNB (cell) may be notified in association with eachother. Here, an RRC connection reconfiguration message is used in thenotification.

The UE that has received the RRC connection reconfiguration message inST3105 uses the DRB release information of a U-plane establishing eNB tobe released in the message to release the DRB configuration of theU-plane establishing eNB in the case where the message includes theinformation indicative of a U-plane release request.

In ST3106, the UE performs the process of disconnecting the connectionwith the U-plane establishing eNB to be released.

In ST3107, the UE, which has completed the process of disconnecting theconnection with the U-plane establishing eNB to be released, notifiesthe C-plane establishing eNB of a connection disconnecting processcomplete message. Here, an RRC connection reconfiguration completemessage is used as the message.

This message may include the DRB configuration complete information ofthe U-plane establishing eNB (cell) to be configured/modified. Here, themessage may include the information indicating that the configuration ofthe modified DRB for the C-eNB is complete.

The C-eNB that has received the connection disconnecting processcomplete message in ST3107 recognizes that the UE has completed theprocess of disconnecting the connection with the U-plane establishingeNB. The C-eNB also recognizes that the UE has performed the process ofmodifying the DRB of the own eNB (cell).

In ST3108, the C-eNB, which has recognized that the UE has completed theprocess of disconnecting the connection with the U-plane establishingeNB, notifies the U-eNB of a connection disconnecting process completemessage. This message may include the identifier of the UE being acommunication target and the identifier of the own eNB (cell). In thisnotification, an X2 interface or a newly provided interface is used, andU-plane connection reconfiguration complete is newly provided as amessage to be notified.

In ST3116, the C-eNB, which has recognized that the UE had performed theprocess of modifying the DRB of the own eNB (cell), notifies the MME ofan E-RAB modification complete message.

In ST3108, the U-eNB that has received the U-plane connectiondisconnecting process complete message performs the process of releasingthe DRB/S1 bearer and, in ST3109, notifies the MME of an E-RAB releasecomplete message. A UE context release complete message may be used inthis notification.

The MME, which has received the E-RAB modification complete message andE-RAB release complete message from the U-plane establishing eNBsincluding the C-eNB in ST3116 and ST3109, can recognize that the releaseof the E-RAB and the modification of the E-RAB of each U-planeestablishing eNB are complete.

In ST3110, the MME that has recognized that the release of the E-RAB ofeach U-plane establishing eNB is complete notifies the S-GW of a messagerequesting to release the S1 bearer. Here, a modify bearer requestmessage is used.

In ST3111, the S-GW that has received the message requesting to releasethe S1 bearer uses the information included in the message to releasethe S1 bearer between the U-plane establishing eNB to be released anditself.

In ST3112, the S-GW that has released the S1 bearer notifies the MME ofan S1 bearer release complete message. Here, a modify bearer responsemessage is used.

Through the processes above, the DRB between the UE and the U-planeestablishing eNB is released, and the S1 bearer between the U-planeestablishing eNB and the S-GW is released. This completes the process ofreleasing a U-plane establishing eNB for the UE being a communicationtarget.

As described above, the U-plane for the UE being a communication targetis connected by the radio bearer 1 (3003) between the UE and the C-eNBand the S1 bearer 1 (3004) between the C-eNB and the S-GW. In ST3005 andST3006, user data is transmitted and received between the UE and theS-GW by the bearers.

Another method is disclosed as the method of releasing the eNB that isestablished only U-plane between the UE being a communication target anditself. The case in which the criteria (7) described above are used willbe disclosed.

If data transmission has not been performed for a long period in theradio section (Uu) between the eNB that has established only the U-planeand the UE being a communication target and the eNB detects time-out,the eNB releases the DRB/S1 bearer established between the UE being acommunication target and itself.

FIG. 32 shows another example sequence of releasing the U-planeestablishing eNB according to the second embodiment. The sequence shownin FIG. 32 is similar to the sequence shown in FIG. 31, and thus, thesame steps will be denoted by the same step numbers and commondescription will be omitted.

In ST3202, the eNB that has established U-plane monitors datatransmission in a radio section (Uu) between the UE being acommunication target and itself. If data transmission has not beenperformed for a long period and the eNB detects time-out, the eNBreleases the DRB/S1 bearer established between the UE being acommunication target and itself.

In ST3203, the U-plane establishing eNB, which has monitored datatransmission in the radio section between the UE being a communicationtarget and itself and has detected data time-out, notifies the MME of amessage requesting to release the E-RAB established by the own eNB forthe UE being a communication target. S1 signaling may be used in thisnotification. This request message may include the informationindicating that the reason of the request is the expiration of a datamonitoring timer, the identifier of the UE for which data time-out hasbeen detected, and the identifier of the own eNB.

The MME that has received the E-RAB release request message in ST3203determines the U-plane establishing eNB that has made notification as aneNB to be released.

In ST3010, the MME performs the E-RAB configuration for the UE being acommunication target of the U-plane establishing eNBs except for an eNBto be released. The MME notifies each U-plane establishing eNB of theE-RAB configuration.

The MME notifies the eNB to be released of a command to release theE-RAB established between the UE being a communication target anditself. ST3114 shown in FIG. 31 may be performed as the subsequentprocesses.

With reference to FIG. 31, upon receipt of ST3105, the UE performs theprocess of disconnecting the connection with a U-plane establishing eNBto be released. This prevents a malfunction caused by a difference injudgment between the U-plane establishing eNB and the UE.

Not limited to the above, in another method, the UE may perform theprocess of disconnecting the connection with a U-plane establishing eNBto be released when detecting data time-out in ST3201. This allows theUE to perform the process of disconnecting the connection with theU-plane establishing eNB at an early stage, and thus does not performthe process of maintaining the unnecessary communication with theU-plane establishing eNB, for example, the synchronization process ormonitoring of the PDCCH or ePDCCH for scheduling, reducing the powerconsumption of the UE.

Another method is disclosed as the method of releasing the eNB that hasestablished only U-plane with the UE being a communication target.

The UE performing monitoring of a radio communication area (radio linkmonitor (RLM)) between each U-plane establishing eNB (cell) and itself.

The UE receives the RS of each U-plane establishing cell to judge thedegradation in the reception quality in the radio communication areausing the reception result of the RS. Five specific examples of the RSare as follows.

(1) RS for tracking

(2) RS for demodulation

(3) CRS

(4) UE-specific RS

(5) Combination of (1) to (4)

The signal equivalent to the RS may be used in place of the RS.

If the reception quality in a radio communication area has fallen belowa predetermined threshold for a predetermined period, the UE judges thedegradation in reception quality. Alternatively, if the receptionquality in a radio communication area has fallen below a predeterminedthreshold for a predetermined period, the UE may reconnect with theU-plane establishing eNB (cell). The UE detects the U-plane establishingeNB (cell), performs synchronization, transmits the PRACH, and receivesthe TA. A maximum value may be provided for the number of trialreconnections to judge the degradation in reception quality if the UEcannot establish connection even after performing reconnections for themaximum value.

The UE that has judged the degradation in reception quality notifies theC-plane establishing eNB that the reception quality in the radiocommunication area has degraded. This notification may include theidentifier of the U-plane establishing eNB such that a U-planeestablishing eNB whose reception quality in a radio communication areahas degraded is apparent.

The C-plane establishing eNB (cell) that has received the deteriorationinformation from the UE notifies the MME of a message requesting todisconnect the radio link with the U-plane establishing eNB whosereception quality has degraded. The message requesting to release theE-RAB may be used as the message requesting to disconnect the radiolink. S1 signaling may be used in this notification. This requestmessage may include the identifiers of the U-plane establishing eNBwhose reception quality has degraded and the UE being a communicationtarget.

The MME that has received the request message selects the notifiedU-plane establishing eNB as an eNB to be released.

The MME performs the E-RAB configuration for the UE being acommunication target of the U-plane establishing eNBs except for an eNBto be released. The MME notifies each of the U-plane establishing eNBsof the E-RAB configuration. The MME also notifies the eNB to be releasedof the command to release the E-RAB established between the UE being acommunication target and itself. The method disclosed above may beapplied in the subsequent processes.

The UE may perform RLM and, at the time when it judges that thereception quality in an radio communication area has degraded, end theconnection with the U-plane establishing eNB whose reception quality hasdegraded. For example, the UE ends the process for synchronization withthe U-plane establishing eNB and ends monitoring of the PDCCH or ePDCCHfor scheduling from the U-plane establishing eNB.

In the case where, for example, the U-plane only establishing eNB isreleased, the timing of the process of disconnecting the connectionbetween the UE and the U-plane establishing eNB may differ from thetiming of switching the path of the S1 bearer between the S-GW and theU-plane establishing eNB.

For example, in the example sequence of releasing the eNB establishingonly U-plane, shown in FIG. 31, the UE performs the process ofdisconnecting the connection with the U-eNB in ST3106. The UE cannotreceive downlink user data from the U-eNB at and after this timing. Atthis time, however, the process of releasing/modifying the S1 bearerpath is not performed by the S-GW in ST3111. That is, the user data istransmitted to the U-eNB with an original path. It is therefore unclearhow downlink user data, transmitted to the U-eNB between the process ofdisconnecting the connection with the U-eNB by the UE and the process ofreleasing/modifying the S1 bearer path by the S-GW, is handled.

Two methods of solving the above-mentioned problem will be disclosedhere.

(1) The user data is discarded.

(2) The user data is forwarded between U-plane establishing eNBs.

In (1), the user data transmitted from the S-GW to the U-planeestablishing eNB to be released is discarded. Control for this processis not particularly performed, causing no control delay, which enablesquick control switching of the S1 bearer path.

In (2), the user data transmitted from the S-GW to the U-planeestablishing eNB to be released is forwarded to the U-plane establishingeNB not to be released. The configuration for forwarding may beperformed between the U-plane establishing eNBs. The configuration forforwarding may be performed via a C-plane establishing eNB. This enablesforwarding of the user data, causing no loss in user data, which enablesquick control switching of the S1 bearer path.

FIG. 33 shows an example sequence of performing data forwarding betweenU-plane establishing eNBs according to the second embodiment. Dataforwarding is performed between the U-eNB and the C-eNB. The sequenceshown in FIG. 33 is similar to the sequence shown in FIG. 31, and thus,the same steps will be denoted by the same step numbers and commondescription will be omitted.

In ST3302, the U-eNB that has performed the DRB release configuration inST3103 buffers the downlink user data from the S-GW received in ST3301.

In ST3303, the U-eNB that has performed the DRB release configuration inST3103 performs a configuration for forwarding user data between theC-eNB and itself.

Here, the C-eNB has established no U-plane connection in some cases. TheU-plane establishing eNB to be released may perform the configurationfor forwarding user data between the U-plane establishing eNB not to bereleased and itself. The MME may notify the identifier of the eNBestablishing the U-plane connection. For example, there may be provideda list of the correspondence between each of the U-plane establishingeNBs and the E-RAB configuration of each of the U-plane establishingeNBs, and the MME may notify U-plane establishing eNB to be released ofthe list. The U-plane establishing eNB to be released can also recognizethe E-RAB configuration of another U-plane establishing eNB.

After the configuration of forwarding the user data between the U-eNBand the C-eNB in ST3303, in ST3304, the U-eNB may forward the user datafrom the S-GW to the C-eNB. The C-eNB that has received the user datatransmits the user data to the UE by a U-plane connection bearer of theown eNB (cell).

The process of ST3304 may be performed after ST3108. The U-eNB forwardsthe user data after recognizing the completion of the process ofdisconnecting the connection by the UE. This prevents such an operationthat the user data is forwarded before the connection is disconnected.

Forwarding of the user data may be ended after all pieces of the userdata received from the S-GW are forwarded. The forwarding configurationfor the C-eNB may be canceled.

Consequently, even if the timing of the process of disconnecting theconnection between the UE and the U-plane establishing eNB differs fromthe timing of switching the path of the S1 bearer for the S-GW, downlinkuser data can be processed reliably, eliminating a malfunction as asystem.

In change of the U-plane establishing cell (eNB) when there is oneU-plane establishing cell (eNB), the U-plane connection for the UE beinga communication target may be disconnected if no contrivance is made.For example, a disconnection occurs in the case where the process ofreleasing a last connected U-plane establishing cell (eNB) is performedand then the process of configuring a new U-plane establishing cell(eNB) is performed. If the U-plane connection is disconnected, thecommunication of user data is stopped, which is inconvenient for theuser. To solve the above-mentioned problem, the method of forwardinguser data described above may be applied. The user data is buffered bythe last connected U-plane establishing eNB, and then, after a new eNBfor U-plane connection is established, the configuration of forwardingthe user data is performed between the last connected U-planeestablishing eNB and the new U-plane establishing eNB. Then, the lastconnected U-plane establishing eNB may forward the user data to the newU-plane establishing eNB. This prevents the communication of the userdata from being stopped. This method is effective in the case where theUE has only the capability to connect with one U-plane establishing eNB.

In the case where the UE has the capability to connect with a pluralityof U-plane establishing cells (eNBs), in another method, the process ofreleasing the last connected U-plane establishing cell (eNB) may beperformed after a new eNB (cell) for U-plane connection is establishedfor the UE being a communication target. Although this causes the UEbeing a communication target to connect with a plurality of U-planeestablishing eNBs (cells), the U-plane connection will not bedisconnected, preventing the communication of the user data from beingstopped.

In this method, the U-plane connection may be performed once via aC-plane establishing eNB (cell). U-plane connection is once establishedfor the UE being a communication target using the C-plane establishingeNB (cell) and, after the process of releasing the last connectedU-plane establishing eNB (cell), performs the process of configuring anew U-plane establishing eNB (cell). After the completion of thisprocess, the U-plane connection in the C-plane establishing cell (eNB)may be disconnected. Similar effects are achieved in this case.Connection is made via the C-plane establishing cell, eliminating theneed for selecting a new U-plane establishing eNB (cell), which enablesthe U-plane connection to be changed to the C-plane establishing eNB(cell) with a low delay. This is effective because a stop of thecommunication due to its degradation can be prevented in the case whereit takes time to select a new U-plane establishing cell.

The method disclosed in this embodiment enables communication of packetdata with a UE being a communication target using a plurality of eNBs,increasing the communication capacity of the UE.

A plurality of eNBs can be used also in the case where cells aredownsized, increasing spectral efficiency, which increases communicationcapacity as a system.

The control process for establishing a plurality of RRC connections isnot required, simplifying the control process, which reduces an amountof signaling and a control delay amount.

The RRC function of the U-plane establishing eNB can be limited, andthus, in the case where, for example, an eNB dedicated for establishingU-plane is configured, the eNB can be configured more easily than aconventional eNB.

The UE mobility control does not need the control process forestablishing a plurality of RRC connections. Therefore, it suffices tochange (establish/modify/release) only the U-plane establishing eNBwithin the coverage of a C-plane establishing eNB (cell), resulting in acontrol process with a lower delay at higher speed. For example, in thecase where the C-plane establishing eNB (cell) is a coverage cell andthe U-plane establishing eNB (cell) is a capacity cell, HO control isnot required between the capacity cells, and it suffices to change(establish/modify/release) only the U-plane establishing eNB.

First Modification of Second Embodiment

In the conventional method, the control information for the UE being acommunication target is transmitted and received between the MME and oneC-plane establishing eNB that is in RRC-connection with the UE. Incontrast, in the method disclosed in the second embodiment, the controlinformation for the UE being a communication target is transmitted andreceived directly between the MME and each U-plane establishing eNB. Thecontrol process for the UE being a communication target by the MMEaccordingly becomes more complicated than the conventional methodprocess.

A first modification of the second embodiment will therefore disclose amethod of performing signaling via a C-plane establishing eNB.

For one communication, one eNB (cell) is used to establish C-planeconnection, and a plurality of eNBs (cells) are used to establishU-plane connection. Signaling between the MME and the U-planeestablishing eNB is performed via the C-plane establishing eNB.

To perform signaling between the MME and the U-plane establishing eNBvia the C-plane establishing eNB, the MME notifies the C-planeestablishing eNB for the UE being a communication target of a signalingforwarding request to each U-plane establishing eNB for the UE being acommunication target. The signaling forwarding request message mayinclude the identifier of the UE (UE-ID) being a communication target.The signaling forwarding request message may include the identifier oraddress of each U-plane establishing eNB (cell), which is a forwardingdestination, for identifying each U-plane establishing eNB (cell) beinga forwarding destination.

The C-plane establishing eNB that has received the signaling forwardingrequest performs the process of forwarding signaling for the UE being acommunication target. The C-plane establishing eNB then forwards thesignaling from the MME to each U-plane establishing eNB and forwards thesignaling from each U-plane establishing eNB to the MME.

The signaling forwarding request may be notified before the MME notifieseach U-plane establishing eNB of the E-RAB configuration of each U-planeestablishing eNB. Alternatively, the signaling forwarding request may benotified simultaneously with the MME notifying each U-plane establishingeNB of the E-RAB configuration of each U-plane establishing eNB. Thesignaling forwarding request may be notified by being included in thesignaling by which the MME notifies each U-plane establishing eNB of theE-RAB configuration of each U-plane establishing eNB.

The method disclosed in this modification allows the signaling betweenthe MME and the U-plane establishing eNB for the UE being acommunication target to be performed via the C-plane establishing eNB.

FIG. 34 shows the architecture according to the first modification ofthe second embodiment. The architecture shown in FIG. 34 is similar tothe architecture shown in FIG. 28, and thus, the same elements will bedenoted by the same numbers and common description will be omitted.

The figure shows the architecture in the case where an eNB dedicated forestablishing U-plane is configured. This architecture may be thearchitecture showing only the UE being a communication target in thismodification.

3401 denotes an S1 interface established between a C-eNB and a U-eNB. Asto the signaling of the UE 2806 being a communication target, the C-eNB2804 has the function of forwarding the signaling from the MME 2803 toeach U-plane establishing eNB 2805 and forwarding the signaling fromeach U-plane establishing eNB 2805 to the MME 2803.

Shown here is the architecture in the case where an eNB dedicated forestablishing U-plane is configured, which eliminates the interface 2815that directly connects between the MME 2803 and the U-eNB 2805, shown inFIG. 28. This is because the signaling between the MME and the U-planeestablishing eNB is performed via the C-plane establishing eNB in thismodification.

The interface 2815 that directly connects the MME and the U-eNB may beprovided in the case where there is a UE that is in C-plane connectionwith the U-eNB, not in the case where an eNB dedicated for establishingU-plane is configured.

Here, the UE (2806) corresponds to a mobile station; the C-eNB (2804), afirst base station; the U-eNB (2805), a second base station; and the MME(2803) and the S-GW (2802), a gateway station. For C-plane signals, theRRC connection between the UE (2806) and the C-eNB (2804) corresponds toa first radio communication connection. Similarly for C-plane signals,the S1-MME signaling connection (2809) between the MME (2803) and theC-eNB (2804) corresponds to a first communication connection. ForU-plane signals, the radio bearer between the UE (2806) and the C-eNB(2804) corresponds to a first radio communication connection, and theradio bearer between the UE (2806) and the U-eNB (2805) corresponds to asecond radio communication connection. Similarly for U-plane signals,the S1 bearer (2814) between the S-GW (2802) and the C-eNB (2804)corresponds to a first communication connection, and the S1 bearer(2813) between the S-GW (2802) and the U-eNB (2805) corresponds to asecond communication connection.

As described above, one communication is performed between the mobilestation and the gateway station by establishing the first communicationconnection between the gateway station and the first base station, thesecond communication connection between the gateway station and thesecond base station, the first radio communication connection betweenthe first base station and the mobile station, and the second radiocommunication connection between the second base station and the mobilestation. This enables a cell change through the addition and release ofcommunication connection and radio communication connection.

The U-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and a second path including the secondcommunication connection and the second radio communication connection.The C-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and a second path including the firstcommunication connection and the second radio communication connection.

Each U-plane establishing eNB 2805 may terminate the S1 interfaces(S1-MMEs) 2809 and 3401, and the C-plane establishing eNB 2804 mayprovide an S1 proxy function between the MME 2803 and each U-planeestablishing eNB 2805. The S1 proxy function forwards the S1 signalingmessage of the UE 2806 being a communication target. The S1 proxyfunction causes the C-plane establishing eNB 2804 to appear to the MME2803 as each U-plane establishing eNB 2805 and causes the C-planeestablishing eNB 2804 to appear to each U-plane establishing eNB 2805 asthe MME 2803.

FIG. 35 shows an example sequence according to the first modification ofthe second embodiment. The sequence shown in FIG. 35 is similar to thesequence shown in FIG. 30, and thus, the same steps will be denoted bythe same step numbers and common description will be omitted.

In ST3010, the MME that has selected the U-plane establishing eNBsconfigures the E-RAB to be established for each of the U-planeestablishing eNBs.

In ST3501, the MME issues an S1 signaling forwarding configurationrequest to the C-plane establishing eNB (C-eNB). Here, this request isan S1-MME proxy configuration request. In ST3502, the C-eNB that hasreceived the request notification performs the configuration for theprocess of forwarding S1 signaling for the UE being a communicationtarget between the U-plane establishing eNB being a forwardingdestination and the MME. Consequently, the S1 message between the U-eNBand the MME is forwarded via the C-eNB.

The C-eNB that has performed the configuration for the forwardingprocess in ST3502 may notify the MME of a message indicative of thecompletion of the forwarding process configuration. The MME canexplicitly confirm the completion, reducing malfunctions. Described hereis the case where there is no such a message. In ST3011, the MMEnotifies an E-RAB modification request message. In ST3503, the MME alsonotifies the C-eNB of an E-RAB configuration request message of theU-plane establishing eNB for the U-plane establishing eNB. Theidentifier or address of the U-plane establishing eNB being a forwardingdestination may be added to the request message or included in therequest message. An S1 message is used as this request message. InST3504, the C-eNB that has received the request message forwards therequest message to the U-plane establishing eNB (U-eNB) using theforwarding configuration in ST3502 and the identifier or address of theU-plane establishing eNB being a forwarding destination. This allows theU-plane establishing eNB (U-eNB) to receive the E-RAB configuration fromthe MME.

Thereafter, each node performs the process of ST3035. The U-eNB that hasreceived the U-plane connection process complete notification from theC-eNB in ST3022 performs the E-RAB configuration process and, in ST3505and ST3506, notifies the MME of the E-RAB configuration complete messagevia the C-eNB. Here, an S1 message is used. The forwarding configurationprocess is performed on the message for the UE, and thus, in ST3506, theC-eNB forwards the message received from the U-eNB in ST3505 to the MME.

Thereafter, the processes from ST3024 to ST3026 and ST3036 areperformed.

Through the processes above, the DRB/S1 bearer is established betweenthe UE and the S-GW using a plurality of eNBs (C-eNB and U-eNB),enabling the transmission and reception of user data.

The method disclosed in this modification prevents a situation in whichthe control information for the UE being a communication target isdirectly transmitted and received between the MME and each U-planeestablishing eNB. Therefore, the control process for the UE being acommunication target by the MME can be prevented from becomingcomplicated.

When the eNB dedicated for establishing U-plane is configured, all thesignalings between the MME and the U-plane establishing eNB can beperformed via the C-plane establishing eNB, eliminating the IF betweenthe MME and the U-plane establishing eNB. This simplifies the systemconfiguration. For example, this method may be applied when a macro eNBand a node dedicated for establishing U-plane, which is directlyconnected with the macro eNB, are configured.

Second Modification of Second Embodiment

In the conventional method, the packet data for the UE being acommunication target is transmitted and received between the S-GW andone C-plane establishing eNB that is RRC-connected with the UE. Incontrast, in the methods disclosed in the second embodiment and thefirst modification of the second embodiment, the packet data for the UEbeing a communication target is directly communicated between the S-GWand each U-plane establishing eNB. Thus, the control process for the UEbeing a communication target in the S-GW becomes more complicated thanthe conventional process.

The second modification of the second embodiment will therefore disclosea method of communicating packet data via a C-plane establishing eNB.

For one communication, one eNB (cell) is used to establish C-planeconnection, and a plurality of eNBs (cells) are used to establishU-plane connection. The data is communicated between the S-GW and eachof the U-plane establishing eNBs via the C-plane establishing eNB.

To communicate packet data between the S-GW and the U-plane establishingeNB via the C-plane establishing eNB, the MME notifies the C-planeestablishing eNB for the UE being a communication target of a packetdata forwarding request to each of the U-plane establishing eNBs for theUE being a communication target.

The packet data forwarding request message may include the identifier ofthe UE (UE-ID) being a communication target. The packet data forwardingrequest message may also include the identifier or address of each ofthe U-plane establishing eNBs (cells) being a forwarding destination foridentifying each of the U-plane establishing eNBs (cells) being aforwarding destination.

As to the packet data for the UE being a communication target, theC-plane establishing eNB that has received the packet data forwardingrequest forwards the packet data from the S-GW to each of the U-planeestablishing eNBs and the packet data from each of the U-planeestablishing eNBs to the S-GW.

The packet data forwarding request may be notified before the MMEnotifies each of the U-plane establishing eNBs of the E-RABconfiguration of each of the U-plane establishing eNBs. Alternatively,the packet data forwarding request may be notified simultaneously withthe MME notifying each of the U-plane establishing eNBs of the E-RABconfiguration of each of the U-plane establishing eNBs. The packet dataforwarding request may be notified by being included in the signaling bywhich the MME notifies each of the U-plane establishing eNBs of theE-RAB configuration of each of the U-plane establishing eNBs.

The MME requests the S-GW to perform packet data communication for theUE being a communication target with each of the U-plane establishingeNBs via the C-plane establishing eNB. The MME requests the S-GW toconfigure the S1 bearer with each of the U-plane establishing eNBs viathe C-plane establishing eNB.

As to the packet data for the UE being a communication target, the S-GW,which has received the request to go through the C-plane establishingeNB, transmits the packet data from the S-GW to each of the U-planeestablishing eNBs via the C-plane establishing eNB and receives thepacket data from each of the U-plane establishing eNBs via the C-planeestablishing eNB.

The method disclosed in this modification allows the packet data betweenthe S-GW and the U-plane establishing eNB for the UE being acommunication target to be communicated via the C-plane establishingeNB.

FIG. 36 shows the architecture according to the second modification ofthe second embodiment. The architecture shown in FIG. 36 is similar tothe architecture shown in FIG. 28, and thus, the same elements will bedenoted by the same numbers and common description will be omitted.

The figure shows the architecture in the case where an eNB dedicated forestablishing U-plane is configured. This architecture may be thearchitecture showing only the UE being a communication target in thismodification.

3601 denotes an S1 interface established between a C-eNB and a U-eNB.

As to the packet data for the UE 2806 being a communication target, theC-eNB 2812 has the function of forwarding the packet data from the S-GW2802 to each of the U-plane establishing eNBs 2805 and forwarding thepacket data from each of the U-plane establishing eNBs 2805 to the S-GW2802.

Shown here is the architecture in the case where an eNB dedicated forestablishing U-plane is configured, eliminating the interface 2813 thatdirectly connects the S-GW 2802 and the U-eNB 2805, shown in FIG. 28.This is because the packet data is communicated between the S-GW and theU-plane establishing eNB via the C-plane establishing eNB in thismodification.

The interface 2813 that directly connects the S-GW and the U-eNB may beprovided in the case where there is a UE that is in C-plane connectionwith the U-eNB, not in the case where an eNB dedicated for establishingU-plane is configured.

Here, the UE (2806) corresponds to a mobile station; the C-eNB (2804), afirst base station; the U-eNB (2805), a second base station; and the MME(2803) and the S-GW (2802), a gateway station. For C-plane signals, theRRC connection between the UE (2806) and the C-eNB (2804) corresponds toa first radio communication connection. Similarly for C-plane signals,the S1-MME signaling connection (2809) between the MME (2803) and theC-eNB (2804) corresponds to a first communication connection, and theS1-MME signaling connection (2815) between the MME (2803) and the U-eNB(2805) corresponds to a second communication connection. For U-planesignals, the radio bearer between the UE (2806) and the C-eNB (2804)corresponds to a first radio communication connection, and the radiobearer between the UE (2806) and the U-eNB (2805) corresponds to asecond radio communication connection. Similarly for U-plane signals,the S1 bearer (2814) between the S-GW (2802) and the C-eNB (2804)corresponds to a first communication connection.

As described above, one communication is performed between the mobilestation and the gateway station by establishing the first communicationconnection between the gateway station and the first base station, thesecond communication connection between the gateway station and thesecond base station, the first radio communication connection betweenthe first base station and the mobile station, and the second radiocommunication connection between the second base station and the mobilestation. This enables a cell change through the addition and release ofcommunication connection and radio communication connection.

The U-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and a second path including the firstcommunication connection and the second radio communication connection.The C-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and the second path including the secondcommunication connection and the second radio communication connection.

Each U-plane establishing eNB 2805 may terminate the S1 interfaces(S1-U) 2814 and 3601, and the C-plane establishing eNB 2804 may providean S1 proxy function between the S-GW 2802 and each U-plane establishingeNB 2805. The S1 proxy function forwards the packet data of the UE 2806being a communication target. The S1 proxy function causes the C-planeestablishing eNB 2804 to appear to the S-GW 2802 as each U-planeestablishing eNB 2805 and causes the C-plane establishing eNB 2804 toappear to each U-plane establishing eNB 2805 as the S-GW 2802.

FIG. 37 shows an example sequence according to the second modificationof the second embodiment. The sequence shown in FIG. 37 is similar tothe sequences shown in FIGS. 30 and 35, and thus, the same steps will bedenoted by the same step numbers and common description will be omitted.

In ST3010, the MME that has selected the U-plane establishing eNBsconfigures an E-RAB to be established for each of the U-planeestablishing eNBs.

In ST3701, the MME issues a user data forwarding request to the C-planeestablishing eNB (C-eNB). Here, the MME issues an S1-U proxyconfiguration request. Here, the MME issues the S1 signaling forwardingconfiguration request together with the user data request. This requestnotification may include the identifier of the UE being a communicationtarget and the identifier of the U-plane establishing eNB (U-eNB) beinga forwarding destination.

In ST3502, the C-eNB that has received the request notification performsthe configuration for the process of forwarding S1 signaling to the UEbeing a communication target between the U-plane establishing eNB beinga forwarding destination and the MME. Thus, the S1 message between theU-eNB and the MME is forwarded via the C-eNB.

In ST3702, the C-eNB also performs the configuration for the process offorwarding user data to the UE being a communication target between theU-plane establishing eNB being a forwarding destination and the S-GW.Thus, the S1 user data between the U-eNB and the S-GW is forwarded viathe C-eNB.

The C-eNB, which has performed the configurations for the processes offorwarding the S1 signaling and S1 user data in ST3502 and ST3702, maynotify the MME of a message indicative of the completion of theforwarding process configuration. The MME can explicitly confirm thecompletion, reducing malfunctions. Described here is the case in whichthere is no such a message as in FIG. 35.

Thereafter, each node performs the processes from ST3011 to ST3506.These processes are shown in FIG. 30 and FIG. 35, which will not bedescribed here.

In ST3703, the MME, which has recognized the completion of the E-RABconfiguration for each of the U-plane establishing eNBs, notifies theS-GW of a message requesting to configure or modify the S1 bearer. Inthis case, a request is issued to configure the path of the S1 bearervia the C-plane establishing eNB. This message may include theidentifier of the UE being a communication target, the identifier ofeach of the U-plane establishing eNBs, the E-RAB configurationinformation of each of the U-plane establishing eNBs, and further, theidentifier of the C-plane establishing eNB that performs forwarding. AnS11 interface may be used in this notification. A modify bearer requestmessage of S11 may be used.

In ST3704, the S-GW, which has received the message requesting toconfigure or modify the S1 bearer via the C-plane establishing eNB,configures or modifies the S1 bearer between each of the U-planeestablishing eNB and itself via the C-plane establishing eNB inaccordance with the information included in the message.

In ST3705, the S-GW that has configured or modified the S1 bearernotifies the MME of an S1 bearer configuration or modification completemessage. An S11 interface may be used in this notification. The modifybearer response message on the S11 may be used.

Through the processes above, a DRB 3027 is established between the UEand the U-plane establishing eNB, and an S1 bearer 3706 is establishedbetween the U-plane establishing eNB and the S-GW via the C-eNB. Thisallows data communications between the UE and the U-eNB and between theU-eNB and the S-GW.

Thereafter, the UE and the U-plane establishing eNB perform theprocesses of ST3029, ST3030, and ST3031.

In ST3707 and ST3708, the user data is transmitted and received betweenthe U-eNB and the S-GW via the C-eNB. In this ease, data may betransmitted to the C-plane establishing eNB on a per-packet basis. Theinformation (such as identifier or address) for identifying the S-GWbeing a forwarding destination, to which the C-plane establishing eNBperforms forwarding, or the U-plane establishing eNB may be added topackets. Each packet can be identified easily when there are a pluralityof forwarding destinations.

In ST3032, user data is transmitted and received between the UE and theU-eNB.

The DRB/S1 bearer is established between the UE and the S-GW using aplurality of eNBs (C-eNB, U-eNB), enabling the transmission andreception of the user data.

The method disclosed in this modification prevents a situation in whichthe packet data for the UE being a communication target is directlytransmitted and received between the S-GW and each of the U-planeestablishing eNBs. This prevents the process of transmitting andreceiving the packet data for the UE being a communication target by theS-GW from becoming complicated.

When an eNB dedicated for establishing U-plane is configured, all thecommunications of packet data between the S-GW and the U-planeestablishing eNB can be performed via the C-plane establishing eNB,eliminating the IF between the S-GW and the U-plane establishing eNB.This simplifies the system configuration. For example, this method maybe applied when a macro eNB and a node dedicated for establishingU-plane, which is directly connected with the macro eNB, is configured.

Third Modification of Second Embodiment

The second embodiment has disclosed the case in which the MME selects aneNB with which a DRB/S1 bearer should be established for the UE being acommunication target. In this modification, in another method, theC-plane establishing eNB selects an eNB with which a DRB/S1 bearershould be established for the UE being a communication target. Thecriteria disclosed in the second embodiment may be applied as thecriteria for selection.

Disclosed below is a method in which a C-plane establishing eNBrecognizes the criteria to select an eNB with which a DRB/S1 bearershould be established for the UE being a communication target.

When the information measured by the UE (also referred to as UEsupported information) is used as the criteria, the UE notifies theC-plane establishing eNB of the information. The method disclosed in thesecond embodiment may be applied as the notification method.

When the information, which is measured or obtained by the network-sidenode, is used as criteria, each node notifies the C-plane establishingeNB of the information. Notification is not required when thenetwork-side node is a C-plane establishing eNB. As in the methoddescribed above, the information for recognizing that the information isof which UE or the information is for which eNB may be included.

The C-plane establishing eNB that has received the information selectsan eNB with which a DRB/S1 bearer should be established for the UE beinga communication target.

The C-plane establishing eNB notifies the MME of a message requesting toestablish an E-RAB using the selected eNB (U-plane establishing eNB).The request message may include the UE identifier (UE-ID) of the UEbeing a communication target, which is identifiable by the MME.Alternatively, the request message may be the mobile subscriber identityidentifiable by the MME. The identifier of the own C-plane establishingeNB (cell) may be included. The UE identifier identifiable by the MMEmay be the UE identifier used in the MME. Still alternatively, therequest message may be the identifier of the C-plane establishing eNB(cell) for the UE and the UE identifier used in the C-plane establishingeNB (cell). S1 signaling may be used for this notification. A newmessage may be provided.

To establish an E-RAB, the MME configures an E-RAB in each U-planeestablishing eNB selected for the UE being a communication target, whichis notified from the C-plane establishing eNB.

The architecture of FIG. 28, disclosed in the second embodiment, isapplicable as the architecture in this modification

FIG. 38 shows an example sequence of establishing/modifying a DRB/S1bearer using a plurality of eNBs according to the third modification ofthe second embodiment. The sequence shown in FIG. 38 is similar to thesequence shown in FIG. 30, and thus, the same steps will be denoted bythe same step numbers and common description will be omitted.

In ST3034, a radio bearer 1 is established between the UE and the C-eNB,and an S1 bearer 1 is established between the C-eNB and the S-GW.

In ST3801, the UE notifies the C-eNB being a C-plane establishing eNB ofa measurement report. The method disclosed in the second embodiment isapplicable in this notification.

In ST3802, the C-eNB that has received the measurement report selects aneNB with which a DRB/S1 bearer should be established for the UE being acommunication target.

In ST3803, the C-plane establishing eNB notifies the MME of a messagerequesting to establish an E-RAB using the selected eNB (U-planeestablishing eNB). In this example, S1 signaling is used in thisnotification, and an E-RAB configuration request message is provided asa new message.

In ST3010, to establish an E-RAB, the MME configures an E-RAB in each ofthe U-plane establishing eNBs selected for the UE being a communicationtarget, which has been notified from the C-plane establishing eNB.

The method disclosed in the example sequence of FIG. 30 is applicable tothe subsequent processes, which will not be described here.

Through the processes above, a DRB/S1 bearer is established between theUE and the S-GW using a plurality of eNBs (C-eNB, U-eNB), and the userdata can be transmitted and received.

FIG. 39 shows an example sequence of releasing a U-plane establishingeNB according to the third modification of the second embodiment. Thesequence shown in FIG. 39 is similar to the sequence shown in FIG. 31,and thus, the same steps will be denoted by the same step numbers andcommon description will be omitted.

In ST3113, a radio bearer 1 is established between the UE and the C-eNB,and an S1 bearer 1 is established between the C-eNB and the S-GW. Aradio bearer 2 (DRB) is established between the UE and the U-eNB, and anS1 bearer 2 is established between the U-eNB and the S-GW.

In ST3901, the UE notifies the C-eNB being a C-plane establishing eNB ofa measurement report. The method disclosed in the second embodiment isapplicable in this notification.

In ST3902, the C-eNB that has received the measurement report determinesa U-plane establishing eNB whose DRB/S1 bearer should be released forthe UE being a communication target. The method of determining a U-planeestablishing eNB to be released by the MME, disclosed in the secondembodiment, is applicable as the method for determination.

In ST3903, the C-plane establishing eNB notifies the MME of a messagerequesting to release the E-RAB established for the UE being acommunication target of the U-plane establishing eNB determined to bereleased. In this example, S1 signaling is used for this notification,and an E-RAB release request message is provided as a new message. Therequest message includes the identifier of the U-plane establishing eNBdetermined to be released, the UE identifier (UE-ID) identifiable by theMME or the mobile subscriber identity identifiable by the MME for the UEbeing a communication target, and the identifier of the own C-planeestablishing eNB (cell).

In ST3010, to establish an E-RAB, the MME configures an E-RAB in each ofthe U-plane establishing eNBs except for the U-plane establishing eNB tobe released, which has been notified from the C-plane establishing eNB.

The method disclosed in the example sequence of FIG. 31 is applicable tothe subsequent processes, which will not be described here.

The MME notifies the U-plane establishing eNB (U-eNB) to be released ofan E-RAB release request message. Notification is made by the MME toallow the same node to control the configuration/modification andrelease of the E-RAB, resulting in simplified control.

Through the processes above, the DRB between the UE and the U-planeestablishing eNB is released, and the S1 bearer between the U-planeestablishing eNB and the S-GW is released. This completes the process ofreleasing a U-plane establishing eNB for the UE being a communicationtarget.

Consequently, U-plane connection for the UE being a communication targetis performed by the radio bearer 1 (3003) between the UE and the C-eNBand the S1 bearer 1 (3004) between the C-eNB and the S-GW. In ST3005 andST3006, the user data is transmitted and received between the UE and theS-GW by the bearers.

FIG. 40 shows another example sequence of releasing the U-planeestablishing eNB according to the third modification of the secondembodiment. The sequence shown in FIG. 40 is similar to the sequenceshown in FIG. 31, and thus, the same steps will be denoted by the samestep numbers and common description will be omitted.

In ST3113, a radio bearer 1 is established between the UE and the C-eNB,and an S1 bearer 1 is established between the C-eNB and the S-GW. Aradio bearer 2 (DRB) is established between the UE and the U-eNB, and anS1 bearer 2 is established between the U-eNB and the S-GW.

In ST4002, the eNB that has established U-plane monitors datatransmission in a radio section (Uu) between the UE being acommunication target and itself. If data transmission has not beenperformed for a long period and the data time-out (expiration of a datamonitoring timer) has been detected, the eNB releases the DRB/S1 bearerestablished between the UE being a communication target and itself. InST4003, the U-plane establishing eNB that has detected data time-outnotifies the C-eNB of a message requesting to release the E-RABestablished by the own eNB for the UE being a communication target. AnX2 signaling may be used for this notification. This request message mayinclude the information showing the expiration of the data monitoringtimer, the identifier of the UE for which the data time-out has beendetected, and the identifier of the own eNB.

In ST4004, the C-eNB that has received the E-RAB release request messagein ST4003 determines a U-plane establishing eNB whose DRB/S1 bearer forthe UE being a communication target should be released. In ST4005, theC-plane establishing eNB notifies the MME of a message requesting torelease the E-RAB established for the UE being a communication target ofthe U-plane establishing eNB determined to be released in ST4004. Inthis example, S1 signaling is used for this notification, and an E-RABrelease request message is provided as a new message. This requestmessage includes the identifier of the U-plane establishing eNBdetermined to be released, the UE identifier (UE-ID) identifiable by theMME or the mobile subscriber identity of the UE being a communicationtarget, which is identifiable by the MME, and the identifier of the ownC-plane establishing eNB (cell).

In ST3010, the MME that has received the E-RAB release request messagein ST4005 configures an E-RAB for the UE being a communication target ofthe U-plane establishing eNBs except for the eNB to be released.

The method disclosed in the example sequence of FIG. 31 is applicable tothe subsequent processes, which will not be described here.

The MME notifies the U-plane establishing eNB (U-eNB) to be released ofthe E-RAB release request message. Notification is made by the MME toallow the same node to configure/modify and release the E-RAB, resultingin simplified control.

Through the processes above, the DRB between the UE and the U-planeestablishing eNB is released, and the S1 bearer between the U-planeestablishing eNB and the S-GW is released. This completes the process ofreleasing the U-plane establishing eNB for the UE being a communicationtarget.

Consequently, U-plane connection for the UE being a communication targetis performed through the radio bearer 1 (3003) between the UE and theC-eNB and the S1 bearer 1 (3004) between the C-eNB and the S-GW. InST3005 and ST3006, user data is transmitted and received between the UEand the S-GW through the bearers.

FIG. 41 shows still another example sequence of releasing the U-planeestablishing eNB according to the third modification of the secondembodiment. The sequence shown in FIG. 41 is similar to the sequenceshown in FIG. 31, and thus, the same steps will be denoted by the samestep numbers and common description will be omitted.

In ST3113, a radio bearer 1 is established between the UE and the C-eNB,and an S1 bearer 1 is established between the C-eNB and the S-GW. Aradio bearer 2 (DRB) is established between the UE and the U-eNB, and anS1 bearer 2 is established between the U-eNB and the S-GW.

In ST4102, the eNB that has established U-plane monitors datatransmission in a radio section (Uu) between the UE being acommunication target and itself. If data transmission has not beenperformed for a long period and data time-out (expiration of a datamonitoring timer) has been detected, the eNB releases the DRB/S1 bearerestablished between the UE being a communication target and itself. InST4103, the U-plane establishing eNB that has detected data time-outnotifies the MME of a message requesting to release the E-RABestablished for the UE being a communication target by the own eNB. Inthis example, S1 signaling is used in this notification, and an E-RABrelease request message is provided as a new message. The requestmessage includes the identifier of the U-plane establishing eNBdetermined to be released, the UE identifier (UE-ID) of the UE being acommunication target, which is identifiable by the MME, or the mobilesubscriber identity identifiable by the MME, and the identifier of theown U-plane establishing eNB (cell). In ST4104, the U-eNB also notifiesthe C-eNB of the E-RAB release request message. This is because theC-eNB needs to recognize the information of the U-plane establishing eNBwhose E-RAB has been released to select the U-plane establishing eNB. X2signaling may be used for this notification. The request message mayinclude the expiration of the data monitoring timer, the identifier ofthe UE for which data time-out has been detected, and the identifier ofthe own eNB.

In ST3010, the MME that has received the E-RAB release request messagein ST4103 configures an E-RAB for the UE being a communication target ofthe U-plane establishing eNBs except for the eNB to be released.

The method disclosed in the example sequence of FIG. 30 is applicable tothe subsequent processes, which will not be described here.

The MME notifies the U-plane establishing eNB (U-eNB) to be released ofan E-RAB release request message. Notification is made by the MME toallow the same node to control the configuration/modification andrelease of the E-RAB, resulting in simplified control.

Through the processes above, the DRB between the UE and the U-planeestablishing eNB is released, and the S1 bearer between the U-planeestablishing eNB and the S-GW is released. This completes the process ofreleasing the U-plane establishing eNB for the UE being a communicationtarget.

Consequently, U-plane connection for the UE being a communication targetis performed by the radio bearer 1 (3003) between the UE and the C-eNBand the S1 bearer 1 (3004) between the C-eNB and the S-GW. In ST3005 andST3006, the user data is transmitted and received between the UE and theS-GW through the bearers.

The C-plane establishing eNB (cell) recognizes UE assisted information.In the second embodiment, the MME needs to recognize the information,complicating control. However, as disclosed in this modification, theC-plane establishing eNB selects a U-plane establishing eNB for the UEbeing a communication target, eliminating the need for the MME torecognize the UE assisted information serving as the criteria forselection. This simplifies the control process, reducing an amount ofsignaling.

The selection of a U-plane establishing eNB can be judged immediatelyafter the notification of the UE assisted information. This leads to asmall delay in the judgment of selecting a U-plane establishing eNB,allowing for the selection of an eNB more suitable for the communicationwith the UE being a communication target.

Third Embodiment

In the first embodiment to the third modification of the secondembodiment, to establish a bearer for U-plane connection using aplurality of eNBs, the plurality of eNBs all have at least the functionrelated to bearer control. This embodiment aims to further simplify theconfiguration of the eNB for U-plane connection.

For one communication, one eNB (cell) is used to establish C-planeconnection, and a plurality of eNBs (cells) are used to establishU-plane connection.

RRC connection is established as C-plane connection, and one or aplurality of dedicated radio bearers are established as U-planeconnection. A DRB may be used as a dedicated radio bearer.

The architecture of FIG. 28 disclosed in the second embodiment isapplicable as the architecture in this embodiment.

In this embodiment, RRC connection is established using the Uu (2810)interface between the C-eNB (2804) and the UE (2806) being acommunication target. In other words, with reference to the figure,C-plane connection indicated by a dashed line is established between theC-eNB (2804) and the UE (2806). Contrastingly, only data (user data)communication is performed using the Uu (2811) interface between theU-eNB (2805) and the UE (2806) being a communication target. In otherwords, only the U-plane connection indicated by a solid line isestablished between the U-eNB (2805) and the UE (2806). U-planeconnection may be established between the C-eNB (2804) and the UE (2806)as in the conventional case.

The interface for U-plane connection 2811 between the U-eNB (2805) andthe UE (2806) is Uu, which may not be a Uu. A new interface having onlythe U-plane connection function may be provided.

In this embodiment, the eNB that establishes only U-plane connection forone communication has no RRC function. In other words, the eNB, whichestablishes only U-plane connection for the UE being a communicationtarget, has no RRC function. The interface (S1-MME) 2815 is notaccordingly used in signaling communication between the U-eNB (2805)with which only U-plane connection is established and the MME (2803) forthe UE (2806) being a communication target. The RRC function of theU-eNB (2805) for the UE being a communication target can be eliminated,simplifying the configuration of the U-eNB.

The S1-U interface between the S-GW and the U-eNB may not be used in thecommunication of the user data for the UE being the communicationtarget, and communication may be performed using the S1-U interfacebetween the S-GW and the C-eNB and the interface between the CeNB andthe U-eNB. The interface (S1-U) 2813 is not used in the communication ofuser data between the U-eNB (2805) which is established only U-planeconnection for the UE (2806) being a communication target and the S-GW(2802). The interface (S1-U) 2814 between the S-GW (2802) and the C-eNB(2804) and the interface 2812 between the C-eNB (2804) and the U-eNB(2805) are used.

FIG. 42 shows the architecture in the case where an eNB dedicated forestablishing U-plane according to the third embodiment is configured.The architecture shown in FIG. 42 is similar to the architecture shownin FIG. 28, and thus, the same elements will be denoted by the samenumbers and common description will be omitted. In the figure, the eNBdedicated for establishing U-plane is the U-eNB (2805). The eNBdedicated for establishing U-plane performs only the communication withthe UE that establishes only U-plane connection.

When the eNB dedicated for establishing U-plane is configured by themethod according to this embodiment, all the signalings between the MME(2803) and the U-eNB (2805) are performed via the C-eNB (2804),eliminating the interface for signaling between the MME (2803) and theU-eNB (2805).

When the communication of the user data for the UE being a communicationtarget is performed through the S1-U interface between the S-GW (2802)and the C-eNB (2804) and the interface between the C-eNB (2804) and theU-eNB (2805) without using the S1-U interface between the S-GW (2802)and the U-eNB (2805), all the communications of packet data between theS-GW (2802) and the U-eNB (2805) can be performed via the C-eNB (2804),eliminating the interface between the S-GW (2802) and the U-eNB (2805).

Consequently, the configuration of an eNB dedicated for establishingU-plane can be simplified. Further, the interface with the MME is notrequired, enabling flexible installation of an eNB dedicated forestablishing U-plane. Further, the interface with the S-GW is also notrequired, eliminating the interface with the core-network-side node.This enables further flexible installation of an eNB dedicated forestablishing U-plane.

Here, the UE (2806) corresponds to a mobile station; the C-eNB (2804), afirst base station; the U-eNB (2805), a second base station; and the MME(2803) and the S-GW (2802), a gateway station. For C-plane signals, theRRC connection between the UE (2806) and the C-eNB (2804) corresponds toa first radio communication connection, and the RRC connection betweenthe UE (2806) and the U-eNB (2805) corresponds to a second radiocommunication connection. Similarly for C-plane signals, the S1-MMEsignaling connection (2809) between the MME (2803) and the C-eNB (2804)corresponds to a first communication connection. For U-plane signals,the radio bearer between the UE (2806) and the C-eNB (2804) correspondsto a first radio communication connection, and the radio bearer betweenthe UE (2806) and the U-eNB (2805) corresponds to a second radiocommunication connection. Similarly for U-plane signals, the S1 bearer(2814) between the S-GW (2802) and the C-eNB (2804) corresponds to afirst communication connection.

As described above, one communication is performed between the mobilestation and the gateway station by establishing the first communicationconnection between the gateway station and the first base station, thefirst radio communication connection between the first base station andthe mobile station, and the second radio communication connectionbetween the second base station and the mobile station. This enables acell change through the addition and release of communication connectionand radio communication connection.

The U-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and a second path including the firstcommunication connection and the second radio communication connection.The C-plane signals are transmitted while being distributed to a firstpath including the first communication connection and the first radiocommunication connection and a second path including the firstcommunication connection and the second radio communication connection.

FIG. 43 shows the protocol stack of the eNB according to the thirdembodiment. The protocol stack shown in FIG. 43 is similar to theprotocol stack shown in FIG. 29, and thus, the same elements will bedenoted by the same numbers and common description will be omitted.

As to the U-eNB (2913), the protocol for the UE that establishes onlythe U-plane connection is shown. The protocol 2914 for C-planeconnection is not configured. The PDCP protocol 2920, the RLC protocol2921, the MAC protocol 2922, and the PHY protocol 2923 have only thefunction for U-plane. In other words, the protocols have only thefunction for establishing a bearer. As indicated by 4301, the C-eNB(2901) and the U-eNB (2913) may be provided with the function forforwarding user data between the C-eNB (2901) and the U-eNB (2913) forthe UE that establishes only the U-plane connection.

In the configuration of an eNB dedicated for establishing U-plane, theprotocol 2914 for establishing C-plane connection needs not to beprovided in the U-eNB 2913, resulting in a simplified configuration.When the user data for the UE being a communication target iscommunicated by the S1-U interface between the S-GW and the C-eNB andthe interface between the CeNB and the U-eNB, the input and outputfunction of an S1-U interface needs not to be provided, resulting in afurther simplified configuration.

Next, a method of establishing a bearer using a plurality of eNBs(cells) will be disclosed.

In this embodiment, the C-plane establishing eNB selects an eNB thatshould establish a DRB for the UE being a communication target. Thecriteria disclosed in the second embodiment may be applied as thecriteria for selection.

The method disclosed in the third modification of the second embodimentmay be applied as the method in which the C-plane establishing eNBrecognizes the criteria for selection of an eNB that should establish aDRB with the UE being a communication target.

The C-plane establishing eNB that has received the information selectsan eNB that should establish a DRB for the UE being a communicationtarget.

The C-plane establishing eNB configures a DRB for the selected eNB(U-plane establishing eNB). This configuration function may be newlyprovided as the RRC function of the C-plane establishing eNB. TheC-plane establishing eNB configures a DRB to be established for eachU-plane establishing eNB, using the E-RAB configuration received fromthe MME. The DRB for U-plane connection is configured to be shared by aplurality of U-plane establishing eNBs. The criteria for selection maybe used in the sharing. When the own eNB is selected as a U-planeestablishing eNB, the own eNB configures a DRB to be established byU-plane establishing eNBs including the own eNB.

If there is an eNB that has configured a DRB, the C-plane establishingeNB modifies the DRB configuration for the eNB.

The same DRB configuration may be configured for each of the eNBs. Ifthere is no change in the E-RAB, the DRB configuration may be the sameas the DRB configuration of the C-plane establishing eNB which hasalready established C-plane.

As the DRB configuration, the DRB identifier, the PDCP configuration,the RLC configuration, the MAC configuration, and the PHY configurationmay be the same. Alternatively, different DRB identifiers may be used.The DRB configuration in each of the eNBs can be handled dedicatedly.

The C-plane establishing eNB notifies each U-plane establishing eNB of aDRB configuration request message. The request message may include DRBconfiguration information. The request message may include theidentifier of the UE being a communication target and the identifier ofthe C-plane establishing eNB (cell). Notification of the modified DRBconfiguration may not be required for the U-plane establishing eNB whoseDRB configuration has no change after the C-plane establishing eNB hasmodified the DRB. An X2 interface may be used or a new interface may beused in the notification of a DRB configuration request message.

A list of the correspondence between each of the U-plane establishingeNBs and the DRB configuration of each of the U-plane establishing eNBsmay be newly provided. The list may be DRB list_U-plane. The C-planeestablishing eNB may notify each of the U-plane establishing eNBs of thelist. This allows each of the U-plane establishing eNBs to recognize theDRB configuration of another U-plane establishing eNB.

Each of the U-plane establishing eNBs notified of a DRB configurationrequest message configures a DRB for the UE being a communicationtarget, using the DRB configuration information of the own U-planeestablishing eNB.

The C-plane establishing eNB notifies the UE of DRB configurationinformation. The C-plane establishing eNB (cell) may use, as the DRBconfiguration information, the information for identifying the DRBconfiguration of which U-plane establishing eNB, such as the identifierof the U-plane establishing eNB (cell) and the DRB configurationinformation of each of the U-plane establishing eNBs. The systeminformation of each of the U-plane establishing eNBs (cells) may benotified. Alternatively, in configuring an ePDCCH for scheduling for theUE being a communication target, each of the U-plane establishing eNBsmay also notify the configuration information of an ePDCCH. Theinformation indicative of a U-plane establishing request may be notifiedtogether. The system information of each of the U-plane establishingeNBs (cells) and the ePDCCH configuration information may be notifiedthe C-plane establishing eNB in advance.

A list of each of the U-plane establishing eNBs and the DRBconfiguration of each of the U-plane establishing eNBs may be provided.The list may be DRB list_U-plane. The C-plane establishing eNB maynotify the UE of the list.

RRC signaling may be used in this notification. A new message may beprovided, or the DRB configuration information and the systeminformation of the U-plane establishing eNB may be included in theexisting RRC message to be notified. An RRC connection reconfigurationmessage or an AS-config message may be used as a specific example of theexisting RRC message. The DRB configuration information and the systeminformation per U-plane establishing eNB may be included in theRadioResourceConfigDedicated information included in the RRC connectionreconfiguration message or AS-config message. The DRB list may beprovided.

Consequently, the UE being a communication target can recognize the eNBthat establishes the U-plane and the DRB configuration between the eNBand the UE.

The UE being a communication target configures a DRB with each of theU-plane establishing eNBs, and performs the process of connecting witheach of the U-plane establishing eNBs (cells).

In successful connection with the U-plane establishing eNB, the UE beinga communication target may notify each of the U-plane establishing eNBsof a connection complete message. The method disclosed in the secondembodiment may be applied as the notification method. Although themethod (1) is applicable, the methods (2) and (3) that are performedwithout going through a MME are also applicable. An amount of signalingcan be reduced.

Each of the U-plane establishing eNBs that has received the connectioncomplete message from the UE performs the process of establishing a DRBwith the UE being a communication target. The complete message of theprocess may be notified the C-plane establishing eNB. There may benotified the completion of the DRB configuration or the modified DRBconfiguration between the UE and the U-plane establishing eNB. Thismessage may include the identifier of the UE (UE-ID) being acommunication target. The message may include the identifier of the ownU-plane establishing eNB (cell).

The DRB between the UE being a communication target and each of theU-plane establishing eNBs is thus established.

The C-plane establishing eNB and each of the U-plane establishing eNBsperform the configuration for forwarding packet data for the UE being acommunication target between the C-plane establishing eNB and theU-plane establishing eNB. An X2 interface may be used or a new interfacemay be provided for forwarding packet data.

The packet data of the UE being a communication target can thus beforwarded between the C-plane establishing eNB and each of the U-planeestablishing eNBs.

Described next is a data transmission method when a plurality of DRBsare established using a plurality of eNBs.

For downlink data transmission, the C-plane establishing eNB calculatesthe ratio of the quality of each link. The C-plane establishing eNBdetermines the final packet distribution ratio to each of the U-planeestablishing eNBs in consideration of the ratio of quality and thetraffic status of each of the cells and, in accordance with the ratio,distributes the received packets to each of the U-plane establishingeNBs. The distribution ratio is constantly determined in accordance withan update of the quality of each link and the traffic data. The C-planeestablishing eNB may use the criteria for selection of a U-planeestablishing eNB to calculate the quality ratio of each link.

Disclosed below is a method of forwarding packets from the C-planeestablishing eNB to each of the U-plane establishing eNBs. The C-planeestablishing eNB does not input the packets received from the S-GW tothe PDCP but distributes and forwards the packets to each of the U-planeestablishing eNBs. In other words, the C-plane establishing eNBdistributes the packets received from the S-GW to each of the U-planeestablishing eNBs and then forwards them transparently. In this case,the forwarded packets are input to the PDCP of each of the U-planeestablishing eNBs and then undergo the process in accordance with thePDCP protocol. Each of the U-plane establishing eNBs adds a sequencenumber (SN) in the PDCP.

In another method, the C-plane establishing eNB inputs the packetsreceived from the S-GW to the PDCP, adds the SN thereto, and thendistributes and forwards the data unit with the SN to each of theU-plane establishing eNBs. The forwarded data unit is input to the PDCPof each of the U-plane establishing eNBs and then undergoes the processin accordance with the PDCP protocol. The SN in the PDCP of each of theU-plane establishing eNBs may or may not be added. The SN is added bythe PDCP of the C-plane establishing eNB, allowing the UE to rearrangethe user data received from each of the U-plane establishing eNBs usingthe SN.

For uplink data transmission, the UE measures the quality of the linkwith the U-plane establishing eNB and calculates the ratio of thequality of each link. Then, the UE distributes the transmitted packetsto the link of each of the eNBs in accordance with the ratio, andtransmits the packets. The UE notifies an amount of transmission datafor each of the eNBs in a buffer status report (BSR) for each eNB, andthen transmits the amount of transmission data in accordance with thescheduling performed by each of the eNBs using the BSR. The distributionratio is constantly determined in accordance with an update of thequality of each link.

The method opposite to that of downlink may be used as the method offorwarding packets from each of the U-plane establishing eNBs to theC-plane establishing eNB. Each of the U-plane establishing eNBsperforms, for the uplink data received from the UE, up to the processaccording to the PDCP protocol to generate packet data, and thenforwards the packet data to the C-plane establishing eNB. In otherwords, the C-plane establishing eNB transparently forwards the packetdata from the U-plane establishing eNB, which is the packet data afterthe PDCP protocol process, to the S-GW. In this case, the forwardedpackets are not input to the PDCP of the C-plane establishing eNB butare transmitted to the S-GW. The S-GW that has received the packet datafrom the C-plane establishing eNB may rearrange the order of the packetdata. Alternatively, the C-plane establishing eNB may rearrange theorder of the packet data before transmitting the packet data from eachof the U-plane establishing eNBs to the S-GW. The C-plane establishingeNB notifies the S-GW of the packet data whose order has beenrearranged.

In another method, each of the U-plane establishing eNBs performs up toprocess according to the PDCP protocol for the uplink data received fromthe UE, and forwards a data unit, to which the SN of the PDCP is added,to the C-plane establishing eNB. The C-plane establishing eNB inputs theforwarded uplink data unit to the PDCP and rearranges the order with theadded SN, using the process for the PDCP protocol, to thereby generatepacket data. The C-plane establishing eNB transmits the packet datawhose order has been rearranged to the S-GW. This eliminates the needfor rearranging packets by the S-GW.

Disclosed below is a method of starting data transmission to the UEbeing a communication target from the U-plane establishing eNB.

Each U-plane establishing eNB may start the process of transmitting datato the UE upon receipt of the message indicative of the completion ofthe connection with the U-plane establishing eNB from the UE or uponcompletion of the U-plane data forwarding configuration with the C-planeestablishing eNB. The UE may start the process of receiving data fromthe U-plane establishing eNB (cell) upon transmission of a connectioncomplete message to the U-plane establishing eNB. This reduces adifference of the timing of starting data transmission and receptionprocess between the UE and the U-plane establishing eNB (cell).

Another method will be disclosed. The U-plane establishing eNB receivesdata from the C-plane establishing eNB and then starts the process oftransmitting data to the UE. The UE detects the U-plane establishing eNB(cell) and performs synchronization therewith, and then starts theprocess of receiving from the U-plane establishing eNB (cell).Alternatively, after the successful RA procedure with the U-planeestablishing eNB (cell), the UE may start the process of receiving fromthe U-plane establishing eNB (cell). For example, this is applicable inthe case where there is no message indicative of the completion of theconnection with the U-plane establishing eNB from the UE. This method isadvantageous in that no explicit trigger is required to start datatransmission and reception and that control is simplified.

The data forwarding configuration may be performed between the C-planeestablishing eNB and the U-plane establishing eNB upon each U-planeestablishing eNB receiving DRB configuration information from theC-plane establishing eNB. In such a case, the data forwardingconfiguration may be performed between the C-plane establishing eNB andthe U-plane establishing eNB before the UE completes the connection withthe U-plane establishing eNB, and downlink data may arrive at theU-plane establishing eNB from the C-plane establishing eNB. Afterreceiving the data from the C-plane establishing eNB, the U-planeestablishing eNB starts the process of transmitting data to the UE. TheUE has yet to complete the connection with the U-plane establishing eNB,and fails to receive the data.

However, the use of retransmission control by the U-plane establishingeNB reduces undeliveries of the data. Besides, increasing the maximumretransmission number in advance eliminates almost all of theundeliveries of the data. The method disclosed here therefore achievesan effect of simplifying control with hardly any undelivery of data.

The methods disclosed in the second embodiment may be applied as themethod in which the UE transmits and receives U-plane data to and fromthe U-plane establishing eNB (cell) and the method in which the UEtransmits and receives the C-plane data and/or U-plane data to and fromthe C-plane establishing eNB (cell).

FIG. 44 shows an example sequence of establishing/modifying a DRB usinga plurality of eNBs according to the third embodiment. The sequenceshown in FIG. 44 is similar to the sequence shown in FIG. 30, and thus,the same steps will be denoted by the same step numbers and commondescription will be omitted.

In ST3034, a radio bearer 1 is established between the UE and the C-eNB,and an S1 bearer 1 is established between the C-eNB and the S-GW.

In ST4401, the UE notifies the C-eNB being a C-plane establishing eNB ofa measurement report. The method disclosed in the third modification ofthe second embodiment can be applied here.

In ST4402, the C-eNB that has received the measurement report selectseNBs that should establish a DRB for the UE being a communicationtarget. The method disclosed in the third modification of the secondembodiment is applicable as the selection method.

In ST4403, the C-plane establishing eNB determines the DRB configurationusing each of the selected eNBs (U-plane establishing eNBs). In thiscase, the DRB configuration may be modified for the U-plane establishingeNB that has established a DRB.

In ST4404, the C-plane establishing eNB configures the DRB of the owncell. The modified DRB may be configured in modification.

In ST4405, the C-plane establishing eNB notifies each of the selectedU-plane establishing eNBs (U-eNBs) of a DRB configuration requestmessage. The request message may include DRB configuration information.Alternatively, the request message may include the identifier of the UEbeing a communication target and the identifier of the C-planeestablishing eNB (cell). An X2 interface may be used or a new interfacemay be provided in the notification of a DRB configuration requestmessage. Here, a U-plane connection configuration message is used.

Each of the U-eNBs, which has been notified of the DRB configurationrequest message, performs the DRB configuration of the own eNB. Each ofthe U-eNBs needs not to perform the DRB configuration by itself becausethe request message includes the configuration information on a DRB tobe established by each U-eNB. Each of the U-eNBs performs the DRBconfiguration using the notified DRB configuration information.

In ST4406, the C-eNB that has configured or modified the DRB in ST4404notifies the UE of the DRB configuration information or the like. Here,an RRC connection reconfiguration message is used in the notification.

If the RRC connection reconfiguration message includes the informationindicative of a U-plane establishment request, the UE that has receivedthe message in ST4406 configures the DRB of each of the U-planeestablishing eNBs using the DRB configuration information of the U-planeestablishing eNB in the message.

In ST4407, the UE starts the process of connecting with the U-planeestablishing eNB.

The processes from ST3018 to ST3022 are similar to the processes shownin FIG. 30, which will not be described here.

Each of the U-eNBs, which has received the DRB establishment completemessage in ST3022, can recognize that a radio bearer (DRB2) (3027) hasbeen configured with the UE.

In ST4408, the C-eNB and each of the U-eNBs perform the configurationfor forwarding packet data for the UE being a communication targetbetween the C-eNB and the U-eNB. This process establishes a link fordata forwarding between the C-plane establishing eNB and the U-planeestablishing eNB. Consequently, in ST4409, the packet data of the UEbeing a communication target can be forwarded between the C-eNB and eachof the U-eNBs.

The processes from ST3029 to ST3032 are similar to the processes shownin FIG. 30, which will not be described here.

Through the processes above, a DRB is established between the UE being acommunication target and a plurality of eNBs (C-eNB, U-eNB), enablingthe transmission and reception of user data.

A method of releasing the eNB that has established only U-plane with theUE being a communication target will now be disclosed. In other words,disclosed below is a method of releasing a DRB established between theeNB to be released and the UE being its communication target.

In this embodiment, the C-plane establishing eNB selects an eNB to bereleased. The criteria for selection may be the criteria when theC-plane establishing eNB selects an eNB that should establish a DRB forthe UE being a communication target. The C-plane establishing eNB usesthe criteria to select an eNB to be released. For example, when thecommunication quality between the UE and the eNB (cell) falls below apredetermined threshold, the C-plane establishing eNB may select the eNBas an eNB to be released.

The C-plane establishing eNB, which has selected a U-plane establishingeNB to be released, stops data forwarding to the U-plane establishingeNB.

The C-plane establishing eNB performs the DRB configuration for the UEbeing a communication target of the U-plane establishing eNBs except foran eNB to be released. The C-plane establishing eNB notifies each of theU-plane establishing eNBs of a DRB configuration request message. An X2interface may be used or a new interface may be provided in thenotification of a DRB configuration request message.

For the eNB that has no change in the DRB configuration after theC-plane establishing eNB has modified the DRB configuration, thenotification of the modified DRB configuration request message may notbe required.

The C-plane establishing eNB notifies an eNB to be released of aninstruction to release the DRB established between the UE being acommunication target and itself. The instruction message may include theidentifier of the UE being a communication target and the identifier ofthe C-plane establishing eNB (cell). An X2 interface may be used or anew interface may be provided in the notification of a DRB releasecommand message.

The eNB to be released, which has received from the C-plane establishingeNB the instruction to release the DRB established between the UE beinga communication target and itself, stops scheduling to the UE. Beforestopping scheduling, the eNB may transmit, to the UE, all of the leftpacket data without being transmitted from the eNB being a releasetarget to the UE. Alternatively, the eNB may complete the retransmissionprocess for all of the packet data whose retransmission process has yetto be complete through HARQ or ARQ.

Each of the U-plane establishing eNBs, which has received the DRBmodification request message, configures the DRB of the own eNB. TheU-plane establishing eNB, which has received the instruction to releasethe DRB established between the UE being a communication target anditself, performs the process of releasing the DRB established betweenthe UE being a communication target and the own eNB.

The method of establishing/modifying a DRB may be applied to the processregarding each of the U-plane establishing eNBs that has received theDRB modification request message.

The C-plane establishing eNB notifies the UE of DRB release information.The C-plane establishing eNB (cell) that notifies the UE of the DRBrelease information notifies the UE being a communication target of theDRB release information of each of the U-plane establishing eNBs and theinformation for identifying the DRB of which U-plane establishing eNB,for example, the identifier of the U-plane establishing eNB, through RRCsignaling. The DRB release information may include the DRB configurationinformation of each of all the U-plane establishing eNBs except for theU-plane establishing eNB to be released by the C-eNB. The information,indicative of a DRB release request for the U-plane establishing eNBdetermined to be released by the C-eNB, may be notified together. Thesystem information of each U-plane establishing eNB (cell) may benotified together. The configuration information of an ePDCCH may benotified together. The information may be available for the UE in thecase where the system information is changed or a U-plane establishingeNB is newly established in the U-plane establishing eNBs except for theU-plane establishing eNB to be released.

An RRC message may be used. An RRC connection reconfiguration message oran AS-config message may be used as a specific example of the RRCmessage. The RadioResourceConfigDedicated information in the RRCconnection reconfiguration message or the AS-config message may be used.

Consequently, the UE being a communication target can recognize therelease of the DRB established between the U-plane establishing eNB tobe released and itself.

The C-plane establishing eNB notifies the UE of the DRB configuration ormodification information of the U-plane establishing eNBs except for theeNB to be released. The information may be included in the RRC messageabove. The DRB configuration or modification information and the DRBrelease information may be included in one message to be notified. Themethod disclosed in the second embodiment is applicable to thesubsequent process of configuring or modifying the DRB of the U-planeestablishing eNBs except for the eNB to be released.

The UE that has received the DRB release information ends the connectionwith each of the U-plane establishing eNBs (cells) that performs DRBrelease. The UE may end monitoring of the PDCCH or ePDCCH of the eNB.

The UE, which has performed the process of releasing the DRB with theeNB to be released and has disconnected the connection therewith, maynotify the eNB of a disconnection complete message. The method (2) or(3) of notifying each of the U-plane establishing eNBs of a connectioncomplete message may be applied as the notification method.

The eNB to be released, which has received the disconnection completemessage from the UE, activates the process of releasing theconfiguration of data forwarding between the C-plane establishing eNBand itself, and performs the process of deactivating the data forwardingconfiguration between the eNB to be released and the C-planeestablishing eNB. When the C-plane establishing eNB receives thedisconnection complete message from the UE, the C-plane establishing eNBactivates the process of deactivating the configuration of the dataforwarding between the eNB to be released and itself, and performs theprocess of deactivating the data forwarding configuration between theeNB to be released and the C-plane establishing eNB.

Consequently, the DRB established between the eNB to be released and theUE being a communication target is released.

The data forwarding method disclosed in the first embodiment may beapplied as the data forwarding, using a plurality of U-planeestablishing eNBs whose DRB has been established between a target UE anditself except for the released eNB.

No data loss is caused in the release of a U-plane establishing eNB.This is because the C-plane establishing eNB performs the DRBconfiguration of each U-plane establishing eNB, switches a path of theuser data, and controls data forwarding. It is therefore not necessaryto particularly perform control for avoiding data loss in the release ofthe U-plane establishing eNB.

FIG. 45 shows an example sequence of releasing a U-plane establishingeNB according to the third embodiment. The sequence shown in FIG. 45 issimilar to the sequences shown in FIGS. 30 and 31, and thus, the samesteps will be denoted by the same step numbers and common descriptionwill be omitted.

A radio bearer 1 (3003) is established between the UE and the C-eNB, andan S1 bearer 1 (3004) is established between the C-eNB and the S-GW. Aradio bearer 2 (DRB) (3027) is established between the UE and the U-eNB.In this example sequence, user data forwarding configuration isperformed between the C-eNB and the U-eNB. Thus, the user data betweenthe C-eNB and the UE is communicated through the direct communicationbetween the C-eNB and the UE in ST3005, data forwarding between theC-eNB and the U-eNB in ST4409, and the user data communication betweenthe U-eNB and the UE in ST3032. The user data communication between theC-eNB and the S-GW is performed in ST3006.

In ST4501, the UE notifies the C-eNB being a C-plane establishing eNB ofa measurement report. The method disclosed in the third modification ofthe second embodiment is applicable in this notification.

In ST4502, the C-eNB that has received the measurement report selects aU-plane establishing eNB whose DRB should be released, that is, aU-plane establishing eNB to be released, for the UE being acommunication target. The method disclosed in the third modification ofthe second embodiment is applicable as the selection method.

In ST4503, the C-plane establishing eNB determines the configuration ofthe DRB of each of the U-plane establishing eNBs except for the U-planeestablishing eNB to be released. In this case, the DRB configuration maybe modified for the U-plane establishing eNB that has performedestablishment.

In ST4504, the C-plane establishing eNB configures the DRB of the owncell. The modified DRB may be configured in modification.

In ST4505, the C-plane establishing eNB stops forwarding the user datato the U-plane establishing eNB to be released.

In ST4506, the C-plane establishing eNB notifies each of the U-planeestablishing eNBs (U-eNBs) to be released of a DRB release commandmessage. Here, a U-plane connection reconfiguration message is used.

Each of the U-eNBs notified of the DRB release command message performsthe process of releasing the DRB of the own eNB.

In ST4507, each of the U-eNBs notified of the DRB release commandmessage stops scheduling of the user data.

In ST4508, the C-eNB that has configured or modified the DRB in ST4504notifies the UE of DRB configuration information. In this case, theinformation includes the information indicative of a DRB release requestfor the U-plane establishing eNB determined to be released by the C-eNB.The information also includes the DRB configuration information of eachof all the U-plane establishing eNBs except for the U-plane establishingeNB to be released by the C-eNB. The information indicative of a DRBrelease request for the U-plane establishing eNB to be released, DRBconfiguration information of each U-plane establishing eNB (cell), theidentifier of each U-plane establishing eNB (cell), the systeminformation of each U-plane establishing eNB (cell), and theconfiguration information of an ePDCCH are notified in association witheach other. An RRC connection reconfiguration message is used in thisnotification.

If the RRC connection reconfiguration message includes the informationindicative of a DRB release request for the U-plane establishing eNB,the UE that has received the message in ST4508 performs the process ofreleasing the DRB of the U-plane establishing eNB to be released in themessage.

In ST4509, the UE starts the process of disconnecting the connectionwith the U-plane establishing eNB to be released.

The processes from ST3107 to ST3108 are similar to the processes shownin FIG. 31, which will not be described here.

In ST4510, between the C-eNB and the U-eNB, the C-eNB and each of theU-eNBs deactivate the configuration for forwarding packet data for theUE being a communication target. This process deactivates the link fordata forwarding between the C-plane establishing eNB and the U-planeestablishing eNB.

The process of ST3115 is similar to the process shown in FIG. 31, whichwill not be described here.

Through the processes above, the DRB between the UE and the U-planeestablishing eNB is released. This completes the process of releasingthe U-plane establishing eNB for the UE being a communication target.

Consequently, the U-plane connection for the UE being a communicationtarget is performed by the radio bearer 1 (3003) between the UE and theC-eNB and the S1 bearer 1 (3004) between the C-eNB and the S-GW. InST3005 and ST3006, the user data is transmitted and received between theUE and the S-GW by the bearers.

Another method will be disclosed as the method of releasing the eNB thathas established only U-plane between the UE being a communication targetand itself. Disclosed below is a case in which the criterion (7)disclosed in the second embodiment are used.

If data forwarding has not been performed for a long period in the radiosection (Uu) between the eNB that has established only the U-plane andthe UE being a communication target and the eNB detects time-out, theeNB releases the DRB established between the UE being a communicationtarget and itself.

The U-plane establishing eNB, which has monitored the data transmissionin the radio section between the UE being a communication target anditself and has detected data time-out (the expiration of a datamonitoring timer), notifies the C-plane establishing eNB of a messagerequesting to release the DRB established for the UE being acommunication target by the own eNB. X2 may be used or a new interfacemay be provided in this notification. The request message may includethe identifier of the UE for which data time-out has been detected, andthe identifier of the own eNB.

The C-plane establishing eNB that has received the request messageselects the U-plane establishing eNB that has made notification as theeNB to be released.

The C-plane establishing eNB configures a DRB for the UE being acommunication target of the U-plane establishing eNBs except for the eNBto be released. The C-plane establishing eNB notifies each of theU-plane establishing eNBs of the DRB configuration. The C-planeestablishing eNB notifies the eNB to be released of the instruction torelease the DRB established between the UE being a communication targetand itself. The method disclosed above may be applied in the subsequentprocesses.

FIG. 46 shows another example sequence of releasing the U-planeestablishing eNB according to the third embodiment. The sequence shownin FIG. 46 is similar to the sequence shown in FIG. 45, and thus, thesame steps will be denoted by the same step numbers and commondescription will be omitted.

In ST4602, the eNB that has established U-plane monitors the datatransmission in the radio section (Uu) between the UE being acommunication target and itself. If data forwarding has not beenperformed for a long period and data time-out (expiration of datamonitoring timer) has been detected, in ST4603, the U-plane establishingeNB stops scheduling of the user data. In ST4604, the U-planeestablishing eNB notifies the C-eNB of the message requesting to releasethe DRB established for the UE being a communication target by the owneNB. In ST4605, the C-eNB that has received the DRB release requestmessage determines the U-plane establishing eNB that has madenotification as the eNB to be released, and configures or modifies theDRB for the UE being a communication target of the U-plane establishingeNBs except for the eNB to be released. In ST4606, the C-eNB stopsforwarding of the user data.

ST4512 shown in FIG. 45 may be performed as the subsequent processes.

Through the processes above, the DRB between the UE and the U-planeestablishing eNB is released. This completes the process of releasingthe U-plane establishing eNB for the UE being a communication target.

Consequently, the U-plane connection for the UE being a communicationtarget is performed by the radio bearer 1 (3003) between the UE and theC-eNB and the S1 bearer 1 (3004) between the C-eNB and the S-GW. InST3005 and ST3006, the user data is transmitted and received between theUE and the S-GW by the bearers.

Not limited to the above, in another method, the UE may perform theprocess of disconnecting the connection with the U-plane establishingeNB to be released when detecting data time-out in ST4601. As a result,the UE can perform the process of disconnecting the connection with theU-plane establishing eNB at an early stage, and thus will not performthe unnecessary process of keeping the communication with the U-planeestablishing eNB, reducing the power consumption of the UE.

Another method will be disclosed as the method of releasing the eNB thathas established only U-plane with the UE being a communication target.

The UE performs monitoring of the radio communication area (radio linkmonitor (RLM)) between each of the U-plane establishing eNBs (cells) anditself. The UE receives the RS of each of the U-plane establishingcells, thereby judging the degradation in the reception quality in theradio communication area using the RS reception result. The exampledisclosed in the second embodiment is applicable as a specific exampleof the RS. Alternatively, a signal equivalent to the RS may be used inplace of the RS.

If the reception quality in the radio communication area has fallenbelow a predetermined threshold for a predetermined period, the UEjudges that the reception quality has degraded. Alternatively, if thereception quality in the radio communication area has fallen below apredetermined threshold for a predetermined period, the UE may reconnectwith the U-plane establishing eNB (cell). The UE detects the U-planeestablishing eNB (cell), synchronizes therewith, transmits the PRACH,and receives the TA. A maximum value may be provided for the number oftrial reconnections to judge the degradation in reception quality if theUE cannot establish connection even after performing reconnections forthe maximum value.

The UE that has judged the degradation in the reception quality notifiesthe C-plane establishing eNB that the reception quality in the radiocommunication area has degraded. This notification may include theidentifier of the U-plane establishing eNB such that reception qualityin a radio communication area of which U-plane establishing eNB hasdegraded can be seen.

The C-plane establishing eNB (cell) that has received the degradationinformation from the UE selects the U-plane establishing eNB whosereception quality has degraded as an eNB to be released.

The C-plane establishing eNB configures a DRB for the UE being acommunication target of the U-plane establishing eNBs except for the eNBto be released. The C-plane establishing eNB notifies each of theU-plane establishing eNBs of the DRB configuration. The C-planeestablishing eNB also notifies the eNB to be released of the instructionto release the DRB established between the UE being a communicationtarget and itself. The method disclosed above may be applied to thesubsequent processes.

The UE may perform RLM and, at the time when it judges that thereception quality in the radio communication area has degraded, maydisconnect the communication with the U-plane establishing eNB whosereception quality has degraded.

The method disclosed in this embodiment enables the communication ofpacket data for the UE being a communication target using a plurality ofeNBs, increasing the communication capacity of the UE.

A plurality of eNBs can be used also when cells are downsized,increasing spectral efficiency, which increases communication capacityas a system.

Besides, the control process for establishing a plurality of RRCconnections is not required, simplifying the control process, whichreduces an amount of signaling and a control delay amount.

The RRC function of the U-plane establishing eNB is not required, andthus, in the case where, for example, an eNB dedicated for establishingU-plane is configured, the eNB can be configured more easily comparedwith a conventional eNB.

The UE mobility control does not need the control process forestablishing a plurality of RRC connections. Therefore, for the coverageof a C-plane establishing eNB (cell), it suffices to change(establish/modify/release) only the U-plane establishing eNB, leading tothe control process with a lower delay at higher speed. For example, inthe case where the C-plane establishing eNB (cell) is a coverage celland the U-plane establishing eNB (cell) is a capacity cell, HO controlis not required between the capacity cells, and only the U-planeestablishing eNB may be changed (established/modified/released).

The MME needs not to recognize the U-plane establishing eNB, and thus,in the change of the U-plane establishing eNB, a signaling amount and acontrol delay amount can be reduced in the control process on thenetwork side. This leads to the control process with much lower delay atmuch higher speed for the UE mobility control.

The S-GW needs not to recognize the U-plane establishing eNB, and thus,in the change of a U-plane establishing eNB, an amount of signaling anda control delay amount can be reduced in the control process on thenetwork side. This leads to the control process with much lower delay atmuch higher speed for the UE mobility control.

The third embodiment has disclosed the method in which the C-planeestablishing eNB selects and determines an eNB that should establish aDRB with the UE being a target. In another method, the MME may selectand determine an eNB that should establish a DRB with the UE.

In this case, the MME may notify the C-plane establishing eNB of theU-plane establishing eNB selected and determined. The C-planeestablishing eNB configures the DRB configuration of the notifiedU-plane establishing eNB.

The method described above is applicable to the subsequent processes.

Unfortunately, this method cannot achieve an effect of eliminating theneed for the MME to recognize the U-plane establishing eNB. However,this method is effective because it achieves other effects.

First Modification of Third Embodiment

In the third embodiment, the C-plane establishing eNB configures the DRBof each U-plane establishing eNB for the UE being a communicationtarget. Thus, a conflict may occur between the DRB configuration and theresource configuration for other UE being served by each U-planeestablishing eNB. This modification will disclose the method of avoidingsuch a conflict.

An eNB for concentrated control (also referred to as a master eNB),which controls specific one or a plurality of eNBs, is provided in aspecific area. The eNB having the RRC function may be an eNB forcentralized control. In this specific area, the UE establishes RRCconnection with the eNB for centralized control. The RRC connection maybe established via another eNB for centralized control.

For the UE being a communication target, the C-plane establishing eNBmay be an eNB for centralized control, and the U-plane only establishingeNB may be an eNB (target eNB for centralized control, slave eNB) thatis controlled by the eNB for centralized control. The eNB forcentralized control controls all the eNBs (C-plane establishing eNB andU-plane establishing eNB) for the UE being a communication target.Specifically, the control may be performed in each protocol of the RRC,PDCP, RLC, MAC, and PHY.

When performing control, the eNB for centralized control performs aconfiguration according to the priority order for the DRBs of other UEsbeing served by the U-plane establishing eNB. The following threespecific examples will be disclosed below.

(1) A DRB of a UE being served by another eNB (cell) has higherpriority.

(2) A DRB of a UE being served by the own eNB (cell) has higherpriority.

(3) A DRB of a UE, for which the own eNB (cell) is a U-planeestablishing eNB, has higher priority.

Specific examples of the DRB configuration include the configuration ofa DRB identifier and the configuration of a lower layer. Examples of thelower layer include the PDCP configuration, RLC configuration, MACconfiguration, and PHY configuration.

When the eNB for centralized control performs control, the U-plane-sideuser data is transmitted between the eNB for centralized control and atarget eNB for centralized control. Disclosed below are seven specificexamples of the layer for this transmission.

(1) IP packet data before being input to PDCP

(2) Data unit to which SN is added in PDCP

(3) Data unit between PDCP and RLC

(4) Data unit between RLC and MAC

(5) Data unit after scheduling in MAC

(6) Data unit before HARQ in MAC

(7) Data unit between MAC and PHY

A link for the transmission of the such data may be established betweenthe eNB for centralized control and the target eNB for centralizedcontrol. This enables the transmission of the U-plane-side user databetween the eNB for centralized control and the target eNB forcentralized control.

The eNB for centralized control may notify each target eNB forcentralized control of the configuration in a required layer or protocolamong the DRB configurations in each target eNB for centralized control.This reduces an amount of signaling.

The method disclosed in this modification is also applicable in the casewhere a plurality of nodes or cells are configured in one eNB, not in aplurality of eNBs. A node or cell for centralized control may beprovided in one eNB. The node or cell for centralized control serves asa C-plane establishing eNB (cell) for the UE being a communicationtarget, and a node or cell in another eNB serves as a U-plane onlyestablishing eNB (cell). The node or cell for centralized control maynot only serve as a C-plane establishing eNB (cell) but also serve as aU-plane establishing eNB (cell) for the UE being a communication target.

FIG. 47 shows the architecture according to a first modification of thethird embodiment, which shows the case in which a cell for centralizedcontrol is provided in one eNB.

4701 denotes an eNB. 4702 denotes a cell that establishes C-planeconnection, which is referred to as a C-cell. 4703 denotes a cell thatestablishes only U-plane connection, which is referred to as a U-cell.The C-cell and the U-cell are configured in the same eNB. 4704 denotes alink for transmitting U-plane-side user data provided between the C-celland the U-cell. 4705 donates an interface for signaling provided betweenthe C-cell and the U-cell. The interface may be X2 or an interface maybe newly provided. The C-cell (4702) serves as a cell for centralizedcontrol and controls all the cells in the same eNB (4701).

In the case where an eNB for centralized control is provided in aspecific area, the eNB in 4701 may denote an eNB in the specific area,the C-cell may denote an eNB for centralized control configured in thespecific area, and the U-cell may denote a target eNB for centralizedcontrol in the specific area.

The method disclosed in this modification achieves the following effectsin addition to the effects of the third embodiment.

An eNB for centralized control is provided in a specific area, allowingthe DRB of each UE to be configured in consideration of all theresources of all the eNBs and all the UEs being served by all the eNBs.

An occurrence of a conflict can be avoided between the DRB configurationof each U-plane establishing eNB for the UE being a communicationtarget, performed by the C-plane establishing eNB, and the resourceconfiguration for another UE being served by each U-plane establishingeNB, performed by each U-plane establishing eNB.

Thus, adjustment is not required between eNBs in a specific area,reducing a control delay and an amount of signaling.

Disclosed below is a method of handling U-plane in the case where aC-plane establishing cell (eNB) is changed for the UE being acommunication target in the second embodiment to the first modificationof the third embodiment. Handover (HO) may be applied to a change of aC-plane establishing eNB. How to handle the case where an eNB forU-plane connection is established for the UE being a communicationtarget is a problem.

The following two are the method in the case where handover for the UEbeing a communication target is performed between different C-planeestablishing eNBs.

(1) U-plane connection is once returned to a C-plane establishing eNBcell.

When the U-plane establishing eNB differs from the C-plane establishingeNB, U-plane connection is changed from the U-plane only establishingeNB to the C-plane establishing eNB (source C-plane establishing eNB)before handover. The U-plane connection with the source C-planeestablishing eNB is established or modified, and the U-plane onlyestablishing eNB is released.

As a result, the U-plane connection for the UE being a communicationtarget is also established by the source C-plane establishing eNB.

In this state, HO is performed from the source C-plane establishing eNBto the C-plane establishing eNB being a target (target C-planeestablishing eNB). The conventional method may be applied in this case.

After HO to the target C-plane establishing eNB, the process ofestablishing U-plane connection may be performed again for the UE beinga communication target.

This process may be performed as required.

In HO of X2 between C-plane establishing eNBs, the MME does notrecognize that HO is to be performed in a HO preparation phase. Thus,when the MME selects a U-plane establishing eNB, the source C-planeestablishing eNB that has determined HO may request the MME to changeU-plane. This request message may include the information indicatingthat a change request is made due to HO. The MME may accordingly performthe process of configuring or modifying the C-plane establishing eNB asa U-plane establishing eNB and perform the process of releasing theoriginally established U-plane only establishing eNB.

As a result, the C-plane establishing eNB can be changed for the UEbeing a communication target without disconnecting the U-planeconnection.

(2) A target C-plane establishing eNB notifies a UE of an eNB thatestablishes U-plane connection.

The source C-plane establishing eNB notifies the target C-planeestablishing eNB of a HO request. This message may include theinformation of the U-plane establishing eNB configured for the UE beinga current HO target.

The target C-plane establishing eNB that has received the informationselects and determines a U-plane establishing eNB that establishesU-plane connection with a UE being a HO target. The U-plane establishingeNB may not be changed.

The target C-plane establishing eNB notifies the source C-planeestablishing eNB of a HO request response message. The message includesthe information of the U-plane establishing eNB configured by the targetC-plane establishing eNB.

The source C-plane establishing eNB notifies the UE of a HO requestmessage together with the information.

The UE changes the C-plane connection to the target C-plane establishingeNB and also changes the U-plane connection with the U-planeestablishing eNB information.

Contrastingly, the target C-plane establishing eNB that has selected anddetermined a U-plane establishing eNB notifies the MME of theinformation in an E-RAB configuration request message. The MME uses theinformation to perform the process of configuring, modifying, orreleasing an E-RAB of the U-plane establishing eNB.

Thus, the C-plane establishing eNB and the U-plane establishing eNB canbe changed for the UE being a communication target.

The C-plane establishing eNB can be accordingly changed for the UE beinga communication target without disconnection of the U-plane connection.

If handover is performed between the cells in a C-plane establishing eNBfor the UE being a communication target, the method in the case where HOis performed between different C-plane establishing eNBs may be appliedbetween cells in the C-plane establishing eNB. This method achievessimilar effects.

Fourth Embodiment

Conventionally, the UE connects with one eNB, and is thus required tonotify a scheduling request (SR) to only the one eNB when notifying thescheduling request (SR) for uplink transmission. In the methodsdisclosed in the first embodiment to the first modification of the thirdembodiment, however, the UE connects with a plurality of eNBs. Thus, theUE is uncertain about an eNB to be notified of the SR.

This embodiment aims to solve the above-mentioned problem.

The SR is transmitted per eNB (cell) connected with the UE. The SR istransmitted per eNB (cell) as required in accordance with the trafficcontrol disclosed in the first embodiment. This allows the transmissionof the UL data to each eNB (cell) in accordance with the traffic controlin the UE.

The configuration information of the SR for a target UE in each eNB(cell) may be dedicatedly notified the UE by each eNB (cell) in advance.

The SR configuration may be performed in the RRC function.

In the first embodiment, the SR configuration may be included in the RRCfunction of each eNB. The conventional notification method is applicableto notifying the UE.

In the second embodiment, the SR configuration may be included in thelimited RRC function of a U-plane establishing eNB. The method ofnotifying the UE of ePDCCH configuration information may be applied asthe method of notifying the UE of the SR configuration information.

In the third embodiment, the SR configuration may be included in the RRCfunction of a C-plane establishing eNB. The C-plane establishing eNBdetermines the SR configuration of each U-plane establishing eNB (cell)and notifies the UE and each U-plane establishing eNB (cell).

As a result, the UE can recognize the SR configuration for each eNB tonotify the SR.

Other methods will be disclosed. Disclosed below are the method ofhandling uplink data and the method of transmitting the SR by the UE.

The UE separately handles the U-plane UL data and the C-plane UL data.

An example of the U-plane UL data is user data, and an example of theC-plane UL data is signaling data. The UE judges which data is to betransmitted.

The following three will now be disclosed as the method of transmittingSR.

(1) For C-plane UL data, SR is transmitted to a C-plane establishingcell (eNB).

(2) For U-plane UL data, SR is transmitted to a U-plane establishingcell (eNB).

(3) Both of C-plane UL data and the U-plane UL data are transmitted tothe C-plane establishing cell (eNB).

In (1), the UE that has judged that the uplink data is the C-plane ULdata transmits the SR to the C-plane establishing cell (eNB). The SRconfiguration in the C-plane establishing cell (eNB) may be used as theSR configuration. If there are a plurality of C-plane establishing cells(eNBs), the SR may be notified each of the C-plane establishing cells(eNBs) which the UL data relates to. Alternatively, any one C-planeestablishing cell (eNB) may be selected, and the SR may be notified theone C-plane establishing cell (eNB). Predetermined criteria forselection may be used to select one C-plane establishing cell (eNB). Forexample, the criteria disclosed in the second embodiment may be used.The best cell (eNB) may be selected. This allows the C-planeestablishing cell (eNB) that has received the SR to perform schedulingof the uplink data for the UE by the own cell (eNB).

In (2), the UE that has judged that the uplink data is the U-plane ULdata transmits the SR to the U-plane establishing cell (eNB). When theU-plane UL data is distributed to each of the U-plane establishing eNBs(cells) in accordance with data traffic control, SR may be transmittedto each of the U-plane establishing cells (eNBs). The SR configurationmay be the SR configuration in each U-plane establishing cell (eNB).This allows each of the U-plane establishing cells (eNBs) that hasreceived the SR to perform scheduling of the uplink data for the UE bythe own cell (eNB).

In (3), the UE judges whether the uplink data is the U-plane UL data orC-plane UL data, and then, transmits the U-plane UL data and the C-planeUL data to the C-plane establishing cell (eNB). The SR configuration inthe C-plane establishing cell (eNB) may be used as the SR configuration.Alternatively, the SR for U-plane UL data and the SR for C-plane UL datamay be provided in another method. For the U-plane UL data, SR istransmitted using the SR configuration for U-plane UL data. For theC-plane UL data, SR is transmitted using the SR configuration forC-plane UL data.

Disclosed below is a method of providing the SR for C-plane UL data andthe SR for U-plane UL data. The SR for C-plane UL data may beidentifiable from the SR for U-plane UL data. For example, a differentinformation bit string pattern is used for each SR. Alternatively, eachSR is multiplied by a different identification code or sequence.Alternatively, a different resource on a frequency axis and/or on a timeaxis is used for each SR notification. Alternatively, an identifier foridentifying whether the UL data is C-plane data or U-plane data isprovided as the information in the SR.

This allows the eNB notified of the SR to explicitly judge whether theSR is for C-plane UL data or for U-plane UL data.

The configuration information of each SR for a target UE in each eNB(cell) may be dedicatedly notified from each eNB (cell) to the UE inadvance. The method above may be used.

In (3), the SR for C-plane UL data and the SR for U-plane UL data may beprovided and the UE may transmit an SR corresponding to each uplink datato allow the C-plane cell (eNB) that has received the SR to judgewhether the SR is for the C-plane UL data or for the U-plane UL data. Itis thus possible to recognize that scheduling should be performed on theC-plane establishing cell (eNB) or scheduling should be performed on theU-plane establishing cell (eNB). For the SR for U-plane UL data, theinformation equivalent to the SR may be notified the U-planeestablishing cell (eNB). A new message may be provided in thisnotification.

The UE can accordingly recognize a cell (eNB) to be notified of the SRfor the generated data. The C-plane establishing cell (eNB) and theU-plane establishing cell (eNB) can recognize what data has beengenerated, allowing the cell (eNB) that has received the SR or theinformation equivalent to the SR to perform scheduling for uplink data.

The method, in which the SR for C-plane UL data and the SR for U-planeUL data are provided and the UE transmits the SR corresponding to eachuplink data, may be applied to the methods (1) and (2) above. Thisallows the eNB that has received the SR to explicitly judge that thedata is which one of the two types of data in accordance with the SR.

Although the method in which the UE separately handles the U-plane ULdata and the C-plane UL data has been disclosed above, the UE may notseparately handle the U-plane UL data and the C-plane UL data.

In this case, the UE transmits the SR to the C-plane establishing cell(eNB) as the method of transmitting the SR. The UE performs transmissionusing the same SR if the uplink data is the U-plane UL data or theC-plane UL data. The SR configuration in the C-plane establishing cell(eNB) may be used as the SR configuration. The C-plane establishing cell(eNB) that has received the SR performs scheduling of the data using theown cell (eNB). The process of establishing U-plane may be performed ifa U-plane is not established.

In the case where the C-plane establishing cell (eNB) can judge that theUL data is the C-plane UL data or the U-plane UL data, the C-planeestablishing cell (eNB) that has received the SR may notify the U-planeestablishing cell (eNB) of the information equivalent to the SR if thereis U-plane uplink data. A new message may be provided in thisnotification. Scheduling may be performed from the U-plane establishingcell (eNB). The UE may transmit data from the U-plane establishing cell(eNB) to the U-plane in accordance with the scheduling from the U-planeestablishing cell (eNB).

As a result, the UE can recognize a cell (eNB) to be notified of the SR.The cell (eNB) that has received the SR or the information equivalent tothe SR can perform scheduling for uplink data.

The C-plane establishing cell (eNB), which has received the SR from theUE being a communication target, may request the MME to perform a newDRB configuration for the UE being a communication target.Alternatively, the C-plane establishing cell (eNB) may newly select aU-plane establishing eNB and request the U-plane establishing eNB toconfigure the DRB. The methods disclosed in the second embodiment to thefirst modification of the third embodiment may be applied depending on asituation. Therefore, communication capacity can be increased for the UEbeing a communication target.

Fifth Embodiment

Conventionally, the UE connects with one eNB, and is thus required tonotify a buffer status report (BSR) to only the one eNB when notifyingthe buffer status report (BSR). In the methods disclosed in the firstembodiment to the first modification of the third embodiment, however,the UE connects with a plurality of eNBs. Thus, the UE is uncertainabout an eNB to be notified of the BSR.

This embodiment aims to solve the problem.

The BSR is transmitted per eNB (cell) to be connected with the UE. TheBSR is transmitted depending on an amount of transmission data per eNB(cell) in accordance with the traffic control disclosed in the firstembodiment. This allows each eNB to perform uplink scheduling to the UEusing the received BSR.

The configuration of the BSR report timing may be included in the RRCfunction.

In the first embodiment, the configuration may be included in the RRCfunction of each eNB. The conventional notification method is applicableto notifying the UE.

In the second embodiment, the configuration may be included in thelimited RRC function of the U-plane establishing eNB. The method ofnotifying the UE of the ePDCCH configuration information may be appliedas the method of notifying the UE of BSR report timing.

In the third embodiment, the configuration may be included in the RRCfunction of the C-plane establishing eNB. The C-plane establishing eNBdetermines the BSR report timing configuration of each U-planeestablishing eNB (cell) and notifies the UE and each U-planeestablishing eNB (cell).

The UE can accordingly recognize the BSR report timing for each eNB,notifying the BSR.

Other methods will be disclosed. Disclosed below are the method ofhandling uplink data and the method of transmitting a BSR by the UE.

The UE separately handles the U-plane UL data and the C-plane UL data.The UE judges which data to be transmitted.

The following three will now be disclosed as the method of transmittingBSR.

(1) For C-plane UL data, BSR is transmitted to a C-plane establishingcell (eNB).

(2) For U-plane UL data, BSR is transmitted to a U-plane establishingcell (eNB).

(3) Both of C-plane UL data and the U-plane UL data are transmitted tothe C-plane establishing cell (eNB).

In (1), the UE that has judged that the uplink data is the C-plane ULdata transmits the BSR to the C-plane establishing cell (eNB). If thereare a plurality of C-plane establishing cells (eNBs), the BSR may benotified each of the C-plane establishing cells (eNBs) which the UL datarelates to. Alternatively, any one C-plane establishing cell (eNB) maybe selected, and the BSR may be notified the one C-plane establishingcell (eNB). Predetermined criteria for selection may be used to selectone C-plane establishing cell (eNB). This allows the C-planeestablishing cell (eNB) that has received the BSR to perform schedulingof the uplink data for the UE by the own cell (eNB).

In (2), the UE that has judged that the uplink data is the U-plane ULdata transmits the BSR to the U-plane establishing cell (eNB). When theU-plane UL data is distributed to each of the U-plane establishing eNBs(cells) in accordance with data traffic control, the BSR may betransmitted to each of the U-plane establishing cells (eNBs). Thisallows each of the U-plane establishing cells (eNBs) that has receivedthe BSR to perform scheduling of the uplink data for the UE in the owncell (eNB).

In (3), the UE judges whether the uplink data is the U-plane UL data orthe C-plane UL data, and then, transmits the U-plane UL data and theC-plane UL data to the C-plane establishing cell (eNB).

The UE may separately handle the U-plane UL data and the C-plane UL datain a logical channel group (LCG) when transmitting the BSR. The LCG forU-plane UL data and the LCG for C-plane UL data are provided. The LCGfor U-plane UL data is configured by the logical channel (LC) to whichthe U-plane UL data is mapped. The LCG for C-plane UL data is configuredby the LC to which the C-plane UL data is mapped.

As a result, the eNB that has been notified of the BSR can explicitlyjudge whether the BSR is the BSR of C-plane UL data or the BSR ofU-plane UL data.

In (3), the LCG for C-plane UL data and the LCG for U-plane UL data maybe provided and the UE may transmit the BSR of the LCG corresponding toeach uplink data to allow the C-plane cell (eNB) that has received theBSR to judge whether the LCG is for the C-plane UL data or for theU-plane UL data. It is thus possible to recognize that scheduling isperformed on the C-plane establishing cell (eNB) or scheduling isperformed on the U-plane establishing cell (eNB). For the BSR of the LCGfor U-plane UL data, the information equivalent to the BSR may benotified the U-plane establishing cell (eNB). A new message may beprovided in this notification.

The UE can accordingly recognize a cell (eNB) to be notified of the BSRfor the generated data. The C-plane establishing cell (eNB) and theU-plane establishing cell (eNB) can recognize what data has beengenerated, allowing the cell (eNB) that has received the uplink datainformation to perform scheduling for uplink data.

The method, in which the LCG for C-plane UL data and the LCG for U-planeUL data are provided and the UE transmits the BSR of the LCGcorresponding to each uplink data, may be applied to the methods (1) and(2) above. This allows the eNB that has received the BSR to explicitlyjudge that the data is which one of the two types of data in accordancewith the BSR.

Other methods will be disclosed as the method of handling uplink dataand the method of transmitting a BSR by the UE.

The target UE separately handles every cell (eNB) to be connectedtherewith. An LCG is configured per cell (eNB). Alternatively, one or aplurality of LCGs may be configured in each cell (eNB). The BSR of theLCG per cell (eNB) may be transmitted to a corresponding cell (eNB).Still alternatively, the BSR may be transmitted to any one C-planeestablishing cell (eNB).

A specific example will be described in which a target UE is connectedto one C-plane establishing cell (eNB) and a plurality of U-planeestablishing cells (eNBs). The LCG is configured per U-planeestablishing cell (eNB). Alternatively, one or a plurality of LCGs maybe configured in each U-plane establishing cell (eNB).

The method of transmitting a BSR will be disclosed.

The BSR of the LCG of the C-plane establishing cell (eNB) is transmittedto the C-plane establishing cell (eNB).

The following two will be disclosed as the method of transmitting theBSR of a U-plane establishing cell (eNB).

(1) The BSR of the LCG of each U-plane establishing cell (eNB) istransmitted to each U-plane establishing cell (eNB).

(2) The BSR of the LCG of each U-plane establishing cell (eNB) istransmitted to the C-plane establishing cell (eNB).

In (1), when the U-plane UL data is distributed to each of the U-planeestablishing eNBs (cells) in accordance with data traffic control, theUE may transmit the BSR to each of the U-plane establishing cells (eNBs)in accordance with the amount of the distributed data. This allows eachof the U-plane establishing cells (eNBs) that has received the BSR toperform scheduling of the uplink data to the UE by the own cell (eNB).

In (2), the BSR may include the information by which the BSR of the LCGof which U-plane establishing cell (eNB) is identifiable. For example,the information may be the identifier of the U-plane establishing cell(eNB). The C-plane cell (eNB) that has received the BSR can judge theBSR of the UL data is of which U-plane establishing cell (eNB). Thisallows the C-plane cell (eNB) to recognize a U-plane establishing cell(eNB) on which scheduling needs to be performed. The C-planeestablishing cell (eNB) may notify the U-plane establishing cell (eNB)of the information equivalent to the BSR. A new message may be providedin this notification.

The UE can accordingly recognize a cell (eNB) to be notified of the BSRfor the generated data.

The above-mentioned method of separately handling the U-plane UL dataand the C-plane UL data in a logical channel group (LCG) in the casewhere the UE transmits a BSR may be combined with the method ofseparately handling the data per cell (eNB) to be connected with atarget UE in that case. The LCG for U-plane UL data and the LCG forC-plane UL data are provided for each cell (eNB) per cell (eNB).

This allows the C-plane establishing cell (eNB) and the U-planeestablishing cell (eNB) to recognize what data has been generated, andthe cell (eNB) that has received the uplink data information can performscheduling in accordance with the uplink data.

Disclosed below are other methods of handling uplink data and anothermethod of transmitting a BSR by a UE.

The U-plane UL data is used separately for every DRB configured by aU-plane establishing cell (eNB).

In a specific example, an LCG is configured for every DRB configured bya U-plane establishing cell (eNB). Alternatively, an LCG may beconfigured in one or a plurality of DRBs configured by a U-planeestablishing cell (eNB). The BSR may include the information foridentifying the BSR of the LCG being of which DRB of which of U-planeestablishing cell (eNB).

The following two will be disclosed as the method of transmitting a BSR.

(1) The BSR of the LCG of the DRB, configured by each U-planeestablishing cell (eNB), is transmitted to each U-plane establishingcell (eNB).

(2) The BSR of the LCG of the DRB, configured by each U-planeestablishing cell (eNB), is transmitted to a C-plane establishing cell(eNB).

This allows the UE to recognize a cell (eNB) to be notified of a BSR forthe generated data. The C-plane establishing cell (eNB) and the U-planeestablishing cell (eNB) can recognize what data has been generated, andthe cell (eNB) that has received the information on the uplink data canperform scheduling according to the uplink data.

Although the method in which a UE separately handles the U-plane UL dataand the C-plane UL data has been disclosed above, the UE maynon-separately handle the U-plane UL data and the C-plane UL data.

In this case, a BSR is transmitted to a C-plane establishing cell (eNB).If there are a plurality of C-plane establishing cells (eNBs), a BSR maybe transmitted to any one of them.

The UE configures an LCG and transmits a BSR to the C-plane establishingcell (eNB).

The C-plane establishing cell (eNB) that has received the BSR performsscheduling on the data using the own cell (eNB). If U-plane has not beenestablished, the process of establishing U-plane is performed.

When the C-plane establishing cell (eNB) can judge whether the UL datais the C-plane or U-plane UL data, if the U-plane uplink data ispresent, the C-plane establishing cell (eNB) that has received the BSRmay notify the U-plane establishing cell (eNB) of the information on theuplink data to perform scheduling from the U-plane establishing cell(eNB). The UE may transmit data from the U-plane establishing cell (eNB)to the U-plane in accordance with the scheduling from the U-planeestablishing cell (eNB).

Consequently, the UE can recognize a cell to be notified of a BSR. Thecell (eNB) that has received the information on the uplink data canperform scheduling for the uplink data.

The C-plane establishing cell (eNB), which has received a BSR from a UEbeing a communication target, may request the MME to configure a new DRBfor the UE being a communication target. Alternatively, the C-planeestablishing cell (eNB) may newly select a U-plane establishing eNB andrequest the U-plane establishing eNB to configure the DRB. The methodsdisclosed in the second embodiment to the first modification of thethird embodiment may be applied depending on situations. Thecommunication capacity for the UE being a communication target can beaccordingly increased.

Sixth Embodiment

As described in the first embodiment, increasing communication capacityis required as a system. For increased communication capacity, it isstudied to downsize cells for higher spectral efficiency. If there are alarge number of small cells, it is complicate to divide the small cellsfor detection or measurement, increasing a control delay. Dividing thesmall cells for detection or measurement is accordantly not suitable formobility control between small cells.

This embodiment aims to reduce the problems above.

A carrier to be used in common (hereinafter, referred to as a sharedcarrier) is configured as a radio resource for a plurality of nodes. Thenode may be an eNB (cell) or a node having none of the functions of theeNB (cell).

Eight features of the shared carrier are as follows.

(1) The same frequency layer is used.

(2) A conventional physical channel for L1/L2 control is not mapped.

(3) Mapping of a physical channel for L1/L2 control of which resourcesare dedicatedly allocated to UEs is allowed.

(4) A physical channel for broadcasting is not mapped.

(5) A detection signal, a synchronization signal, and a reference signalare configured in the same manner irrespective of whether the signalsare configured by any node.

(6) Identifiers for node identification, which are the same, may beincluded.

(7) Shared carriers respectively configured by nodes are in precisesynchronization.

(8) Combination of (1) to (7).

For (2), specific examples of the conventional physical channel forL1/L2 control include PDCCH, PCFICH, and PHICH.

For (3), specific examples of the UE-dedicated physical channel forL1/L2 include ePDCCH and ePHICH.

For (4), examples of the physical channel for broadcasting include PBCH.

For (5), specific examples of the detection signal, the synchronizationsignal, and the reference signal include PSS, SSS, and CRS,respectively. As a specific example of the same configuration, the samecode is used, or a configuration is made on the same symbol.

For (6), a specific example of the identifier for node identificationmay be a cell identifier (cell-ID).

For (7), a specific example of the precise synchronization may be aphase synchronization.

Only the U-plane-side user data may be scheduled to a shared carrier.However, the scheduling information on the U-plane-side user data may bemapped. In this case, another carrier may be used for a radio resourcefor C-plane.

A shared carrier may be used by a node that establishes only U-plane(such as a U-plane only establishing eNB (cell)). The C-planeestablishing node (such as a C-plane establishing eNB (cell)) is causedto have a carrier different from a shared carrier. In this case, it isnot always necessary to synchronize the shared carrier and the carrierfor C-plane establishing node. This operation method may be applied tothe C-plane establishing eNB (cell) and the U-plane only establishingeNB (cell), disclosed in the second embodiment to the first modificationof the third embodiment.

FIG. 48 is a conceptual diagram of shared carriers according to a sixthembodiment. 4801 and 4802 denote C-plane establishing eNBs, and 4805 and4806 denote U-plane only establishing eNBs. The C-plane establishing eNB4801 is connected with the U-plane only establishing eNB 4805 by aninterface 4803. The C-plane establishing eNB 4802 is connected with theU-plane only establishing eNB 4806 by an interface 4804. The interfaces4803 and 4804 may be X2 or other interfaces.

As indicated by 4808, the C-plane establishing eNB 4801 configures acarrier of a frequency layer F1 and uses the carrier as a radio resourcefor a UE being a communication target. As indicated by 4809, the C-planeestablishing eNB 4802 configures a carrier of a frequency layer F2 anduses the carrier as a radio resource for the UE being a communicationtarget.

As indicated by 4810, the U-plane only establishing eNB 4805 configuresa shared carrier of a frequency layer Fm and uses the shared carrier asa radio resource for the UE being a communication target. As indicatedby 4811, the U-plane only establishing eNB 4806 configures a sharedcarrier of the frequency layer Fm and uses the shared carrier as a radioresource for the UE being a communication target.

The carriers of the frequency layer Fm, configured by the U-plane onlyestablishing eNBs 4805 and 4806, are shared carriers.

The shared carriers configured by the U-plane only establishing eNBs4805 and 4806 in a specific area 4807 are in precise synchronization.

4812 denotes a detection signal and/or a synchronization signal and/or areference signal of the shared carrier, and the same signal isconfigured by the U-plane only establishing eNBs 4805 and 4806.

Using the shared carrier as the radio resource by the U-plane onlyestablishing eNBs 4805 and 4806 allows, for example, the use of theshared carrier configured by the U-plane only establishing eNB 4806 as aradio resource for the UE without the need for the UE being acommunication target for the U-plane only establishing eNB 4805 todetect the shared carrier configured by the U-plane only establishingeNB 4806 and achieve synchronization with the shared carrier.

For example, the processes for detection and synchronization of acarrier are not required also in the case where a U-plane onlyestablishing eNB (cell) is changed, disclosed in the second embodiment.

The use of a shared carrier eliminates the need for detecting andmeasuring another carrier also in the measurement by the UE, simplifyingcontrol.

For example, also in the case where the communication quality of thecell through the measurement by the UE is used as the criteria forselection, disclosed in the second embodiment, the UE is merely requiredto measure a shared carrier also in the measurement of the communicationquality of the own cell and another cell, simplifying control.

Thus, configuring a shared carrier can simplify the control for changinga U-plane establishing eNB (cell) while a UE is moving.

In the case where a shared carrier is configured in a small cell, thecarriers of a large number of small cells need not to be divided fordetection or measurement, simplifying control, which reduces a controldelay.

The shared carrier is configured in the same frequency layer, and thus,the use of a shared carrier in a small cell leads to high communicationcapacity achieved as a system without a reduction in spectral efficiencydue to downsized cells.

As the criteria for selecting a U-plane establishing eNB (cell) for theUE being a communication target, the criteria except for thecommunication quality between each U-plane establishing eNB (cell) andthe UE may be used among the criteria disclosed in the secondembodiment. This is because U-plane establishing eNBs (cells) cannot bedistinguished from each other in accordance with the communicationquality of the shared carrier used as the communication quality betweeneach U-plane establishing eNB (cell) and the UE. For example, the UElocation information may be used as another criterion. A U-planeestablishing eNB (cell) to be selected may be judged by using the UElocation information together with the location information of eachU-plane establishing eNB.

In the case where a shared carrier is configured in U-plane onlyestablishing eNBs connected to different C-plane establishing eNBs,radio resources to be allocated to the shared carriers may conflictbetween the UEs being communication targets. For example, a resourceblock on the shared carrier, to which the radio resource for the UEbeing a communication target in the U-plane only establishing eNB 4805,may be the same as the resource block on the shared carrier, to whichthe radio resource for the UE being a communication target is allocatedin the U-plane only establishing eNB 4806. In other words, a conflictoccurs. This is because scheduling is performed dedicatedly andindependently in establishment of each U-plane.

In such a case, the U-plane only establishing cell may performretransmission control such as HARQ or ARQ between the UE being acommunication target and itself. The retransmission control may be madesuch that scheduling can be performed again from a frequency and/or timestandpoint. Even if the above-mentioned conflict occurs, scheduling to anew resource block through retransmission control can reduce a fear ofconflict in the next transmission. The above-mentioned conflict cantherefore be reduced.

Measurement by the UE may be used in another method of reducingconflict. The UE measures the communication quality between a U-planeonly establishing eNB and itself. In configuring a shared carrier, theUE measures the communication quality in the shared carrier. If thecommunication quality of the resource block allocated to the own UE ispoor, another U-plane only establishing cell may be using this resourceblock. Thus, the U-plane only establishing cell, which has received themeasurement result indicative of poor communication quality from the UEvia the C-plane establishing eNB, can avoid allocating this resourceblock to the UE.

Consequently, a conflict of the radio resources scheduled between theU-plane only establishing eNBs can be reduced.

Although the communication quality has been disclosed as to themeasurement of a shared carrier by the UE, besides, the thermal noisepower in a shared carrier may be measured. The thermal noise power maybe measured in units of a predetermined number of PRBs or in units of apredetermined number of subcarriers. The UE may measure the thermalnoise power and notify the U-plane only establishing cell via theC-plane establishing cell as a measurement result.

In another example, a U-plane only establishing cell may performdownlink measurement. In other words, a shared carrier is measured.Measurement may be performed in a subframe for which scheduling is notperformed. Or, a scheduling gap may be provided to enable themeasurement.

This measurement reduces a conflict of radio resources to be scheduledbetween U-plane only establishing eNBs.

FIG. 49 shows an example configuration of the shared carrier in the sameeNB, which shows the case in which a C-plane establishing cell andU-plane only establishing cells are configured in the same eNB. 4901denotes a C-plane establishing cell (C-cell), and 4903 denotes a U-planeonly establishing cell (U-cell). The eNB is configured of the C-planeestablishing cell 4901 and a plurality of U-plane only establishingcells 4903. 4902 denotes the coverage by the C-plane establishing cell4901, and 4904 denotes the coverage by the U-plane only establishingcell 4903. 4905 denotes an interface between the C-plane establishingcell 4901 and each U-plane only establishing cell.

The carrier of a frequency layer F1 is configured as a radio resource inthe C-plane establishing cell, and the shared carrier of a frequencylayer Fm is configured as a radio resource in each U-plane onlyestablishing cell.

The UE being a communication target for each U-cell can accordantly movewithout performing the reconnection process such as the detection andsynchronization in a radio section between a U-cell and itself.

Schedulings of radio resources for a C-cell and a plurality of U-cellsare performed in a unified manner because they are in the same eNB. Forexample, scheduling may be performed by a MAC in the C-cell. Therefore,in a plurality of U-cells, the allocation of the radio resources to theshared carrier for the UE being a communication target for each U-cellcan be scheduled without conflict.

FIG. 50 shows an example configuration of a shared carrier in differenteNBs, which shows a case in which C-plane establishing cell and aU-plane only establishing cell are configured in an eNB. 5002 and 5003each denote a C-plane establishing cell (C-cell), and 5004 and 5005 eachdenote a U-plane only establishing cell (U-cell). The eNB 1 isconfigured of the C-plane establishing cell 5002 and the U-plane onlyestablishing cell 5004. The eNB 2 is configured of the C-planeestablishing cell 5003 and the U-plane only establishing cell 5005.

5008 and 5009 denote the coverages by the C-plane establishing cells5002 and 5003, respectively, and 5010 and 5011 denote the coverages bythe U-plane only establishing cells 5004 and 5005, respectively.

5012 and 5013 each denote an interface between the C-plane establishingcell and the U-plane only establishing cell.

A carrier of a frequency layer F1 is configured as a radio resource inthe C-plane establishing cells 5002 and 5003, and a shared carrier of afrequency layer Fm is configured as a radio resource in the U-plane onlyestablishing cells 5004 and 5005.

In the example configuration, an eNB for centralized control 5001 forcontrolling the eNB 1 and the eNB 2 in a concentrated manner isconfigured. 5006 and 5007 denote an interface provided between the eNBfor centralized control 5001 and the C-plane establishing cell 5002 ofthe eNB 1 and an interface between the eNB for centralized control 5001and the C-plane establishing cell 5003 of the eNB 2, respectively.

The use of a shared carrier allows the UE being a communication targetin each U-cell to move without performing the reconnection process suchas detection and synchronization in a radio section between the U-celland itself.

To configure an eNB for centralized control, radio resources arescheduled in a unified manner in the C-cells and the U-cells of the eNB1 and the eNB 2. The MAC of the eNB for centralized control may performscheduling. Therefore, the allocation of the radio resources to theshared carriers for the UE being a communication target for each U-cellcan be scheduled without conflict.

FIG. 51 shows an example configuration in the case where a sharedcarrier is configured in a specific area, which shows the case in whicha C-plane establishing cell and U-plane only establishing cells areconfigured in an eNB.

5104 and 5108 each denote a C-plane establishing cell (C-cell), and5105, 5106, and 5107 denote a plurality of U-plane only establishingcells (U-cells).

An eNB 1 is configured of the C-plane establishing cell 5104 and theplurality of U-plane only establishing cells 5105 and 5106. An eNB 2 isconfigured of the C-plane establishing cell 5108 and the plurality ofU-plane only establishing cells 5106 and 5107.

5109 and 5116 denote the coverages by the C-plane establishing cells5104 and 5108, respectively, and 5110, 5111, and 5112 denote thecoverages by the U-plane only establishing cells 5105, 5106, and 5107,respectively.

The plurality of U-plane only establishing cells 5105 are installed in aspecific area 5113, the plurality of U-plane only establishing cells5106 are installed in a specific area 5114, and the plurality of U-planeonly establishing cells 5107 are installed in a specific area 5115.

5120, 5121, 5122, and 5123 each denote an interface between the C-planeestablishing cell and the U-plane only establishing cell.

The plurality of U-plane only establishing cells installed in thespecific area 5114 are connected to both of the C-plane establishingcells 5104 and 5108.

A carrier of a frequency layer F1 is configured as a radio resource inthe C-plane establishing cell 5104, a carrier of a frequency layer F2 isconfigured as a radio resource in the C-plane establishing cell 5108,and a shared carrier of a frequency layer Fm is configured as a radioresource in each of the U-plane only establishing cells 5105, 5106, and5107.

In this example configuration, a U-plane eNB for centralized control isconfigured, which controls the U-plane side of a plurality of U-planeonly establishing cells installed in a specific area in a concentratedmanner. As a specific example of the concentrated control on the U-planeside, the user data of each U-plane only establishing cell installed ineach specific area is scheduled. The U-plane eNB for centralized controlmay be provided together with another node without being provided in aphysically dedicated manner. The function of the U-plane eNB forcentralized control may be provided to be included as the function ofanother node. For example, the function may be provided to any one ofthe U-plane establishing cells. This allows a U-plane eNB forcentralized control to be physically installed with ease.

A U-plane eNB for centralized control 5101 schedules pieces of user dataof the plurality of U-plane only establishing cells 5105 installed inthe specific area 5113. A U-plane eNB for centralized control 5102schedules pieces of user data of the plurality of U-plane onlyestablishing cells 5106 installed in the specific area 5114. A U-planeeNB for centralized control 5103 schedules pieces of user data of theplurality of U-plane only establishing cells 5107 installed in thespecific area 5115.

The plurality of U-plane only establishing cells 5106 installed in thespecific area 5114 are connected to the C-plane establishing cell 5104of the eNB 1 as well as the C-plane establishing cell 5108 of the eNB 2.Thus, the U-plane eNB for centralized control 5102 performs schedulingfor UEs including the UEs being served by the C-plane establishing cell5104, which use the C-plane establishing cell 5104 and the U-plane onlyestablishing cells 5106, and the UEs being served by the C-planeestablishing cell 5108, which use the C-plane establishing cell 5108 andthe U-plane only establishing cells 5106.

5117, 5118, and 5119 denote interfaces provided between the U-plane eNBfor centralized control 5101 and each of the U-plane only establishingcells 5105, between the U-plane eNB for centralized control 5102 andeach of the U-plane only establishing cells 5106, and between theU-plane eNB for centralized control 5103 and each of the U-plane onlyestablishing cells 5107, respectively.

The use of a shared carrier in a plurality of U-plane only establishingcells installed in a specific area allows the UE being a communicationtarget in each U-cell to move in the specific area without performingthe reconnection process such as detection and synchronization in aradio section between the U-cell and itself.

Although a shared carrier of the same frequency layer Fm is configuredin the specific areas 5113, 5114, and 5115 in this exampleconfiguration, a shared carrier of a different frequency layer may beconfigured in each of the specific areas. For example, the sharedcarrier of the frequency layer F1 may be configured in each of theU-plane only establishing cells 5105 installed in the specific area5113, the shared carrier of the frequency layer Fm may be configured ineach of the U-plane only establishing cells 5106 installed in thespecific area 5114, and the shared carrier of a frequency layer Fn maybe configured in each of the U-plane only establishing cells 5107installed in the specific area 5115. The use of different frequencylayers reduces conflict between specific areas. Precise synchronizationis not required between shared carriers of different frequencies, and adetection signal and/or a synchronization signal and/or a referencesignal may not be the same between shared carriers of differentfrequencies.

To configure a U-plane eNB for centralized control per specific area,the radio resources of the U-plane only establishing cells installed ineach specific area are scheduled in a unified manner. Scheduling may beperformed by the MAC of the U-plane eNB for centralized control. Thus,the allocation of the radio resources for the UE being a communicationtarget in the U-plane only establishing cells in each specific area canbe scheduled without conflict. The UEs being communication targets forthe U-plane only establishing cells 5106 installed in the specific area5114 include the UE being served by the eNB 1 and the UE being served bythe eNB 2. The allocations of radio resources for both of the UEs can bescheduled to a shared carrier without conflict.

FIG. 52 shows another example in the case where a shared carrier isconfigured in a specific area, which shows the case in which a C-planeestablishing cell and U-plane only establishing cells are configured inan eNB. Part (a) of FIG. 52 is shown in FIG. 51, which will not bedescribed here. Part (b) of FIG. 52 will be described here.

5202 and 5203 each denote a C-plane establishing cell (C-cell), and 5204and 5206 denote a plurality of U-plane only establishing cells(U-cells).

The eNB 1 is configured of the C-plane establishing cell 5202 and theplurality of U-plane only establishing cells 5204. The eNB 2 isconfigured of the C-plane establishing cell 5203 and the plurality ofU-plane only establishing cells 5206.

5205 and 5207 denote the coverages by the U-plane only establishingcells 5204 and 5206, respectively.

The coverages by the C-plane establishing cells 5202 and 5203 are notshown here.

The plurality of U-plane only establishing cells 5204 and 5206 areinstalled in a specific area 5210.

5208 and 5209 each denote an interface between the C-plane establishingcell and the U-plane only establishing cell.

The frequency carriers configured as radio resources in the C-planeestablishing cells 5202 and 5203 are not shown here. The frequencycarriers are as in FIG. 51. The carrier of the frequency layer F1 isconfigured as a radio resource in the C-plane establishing cell 5202,and the carrier of the frequency layer F2 is configured as a radioresource in the C-plane establishing cell 5203.

In each of the U-plane only establishing cells 5204 and 5206, the sharedcarrier of the frequency layer Fm is configured as a radio resource.

A U-plane eNB for centralized control 5201 schedules pieces of user dataof the plurality of U-plane only establishing cells installed in thespecific area 5210.

The U-plane eNB for centralized control 5201 is connected to each of theU-plane only establishing cells 5204 connected to the C-planeestablishing cell 5202 of the eNB 1 and each of the U-plane onlyestablishing cells 5206 connected to the C-plane establishing cell 5203of the eNB 2, the cells being installed in the specific area 5210. TheU-plane eNB for centralized control 5201 accordingly performs schedulingfor UEs including UEs being served by the C-plane establishing cell5202, which use the C-plane establishing cell 5202 and the U-plane onlyestablishing cell 5204, and UEs being served by the C-plane establishingcell 5203, which use the C-plane establishing cell 5203 and the U-planeonly establishing cell 5206.

5211 denotes an interface provided between the U-plane eNB forcentralized control 5201 and each of the U-plane only establishing cells5204 and 5206.

A shared carrier is used in a plurality of U-plane only establishingcells installed in a specific area, allowing the UE being acommunication target for each U-cell to move in the specific areawithout performing the reconnection process such as detection andsynchronization in a radio section between the U-cell and itself

To configure a U-plane eNB for centralized control in a specific area,scheduling of radio resources in a U-plane only establishing cellsinstalled in the specific area may be performed in a unified manner. TheMAC of the U-plane eNB for centralized control may perform scheduling.

Therefore, the allocation of the radio resources to the shared carriersfor the UE being a communication target for the U-plane onlyestablishing cell in the specific area can be scheduled withoutconflict.

In particular, the UEs being communication targets for the U-plane onlyestablishing cells 5204 and 5206 installed in the specific area 5210include the UE being served by the eNB 1 and the UEs being served by theeNB 2. The allocation of the radio resources to the shared carrier forthese UEs can be scheduled without conflict.

Description will be given of the synchronization in the case where ashared carrier is configured in a specific area. In part (b) of FIG. 52,the shared carrier configured by each U-plane only establishing cell5204 and 5206 is synchronized. The synchronization may be precisesynchronization. Two specific examples of the method of achievingprecise synchronization are as follows.

(1) A reference signal source is provided.

(2) A GPS is provided.

In (1), one reference signal source may be provided in a specific areato be connected to each U-plane only establishing cell. The referencesignal source is used for a shared carrier configured by each U-planeonly establishing cell. A reference clock may be generated from thereference signal source. One reference signal source may be provided inthe U-plane eNB for centralized control. The U-plane eNB for centralizedcontrol 5201 is connected with each U-plane only establishing eNB 5204and 5206 by the interface 5211, and thus, is physically connected inmany cases. Thus, the physical connection allows one reference signalsource to be connected to each U-plane only establishing eNB.

The reference signal source may be provided in another node, which isnewly provided, without being provided in the U-plane eNB forcentralized control. The node is physically connected to each U-planeonly establishing cell in a specific area.

In the case where a shared carrier is configured for a plurality ofU-plane only establishing cells in the same eNB as in FIG. 49, thereference signal source may be provided in a C-plane establishing eNB.The C-plane establishing eNB is physically connected to the U-planeestablishing eNB.

Precise synchronization can be accordingly achieved between U-plane onlyestablishing cells in a specific area.

In (2), each U-plane only establishing cell in a specific area isprovided with a GPS, and synchronization is achieved by the GPS. Thiseliminates the need for providing the same reference signal source forphysical connection with each U-plane only establishing cell, allowing aplurality of U-plane only establishing cells to be installed flexibly.

Seventh Embodiment

A problem solved in the seventh embodiment will be described below. Inthe configuration described in the first modification of the thirdembodiment, one eNB or central entity schedules the data to betransmitted on a radio link and transmits the data. In thisconfiguration, time scheduling is performed as well, and thus, precisesynchronization is required in eNBs that actually perform transmissionon a radio link. However, it is difficult to achieve precisesynchronization among a large number of eNBs. Synchronization isgenerally achieved using a GPS or the network time protocol (NTP) of anetwork, leading to a problem that, for example, a GPS receiver needs tobe mounted, an eNB is difficult to be installed in a place where radiowaves from the GPS can be received, or synchronization with preciseaccuracy is difficult to be achieved in the NTP.

A solution in the seventh embodiment will be described below. To solvethe above-mentioned problem, scheduling on a radio link is performedwhile being divided into a “node that performs concentrated control” anda “node that actually performs transmission,” to thereby performscheduling in a unified manner without achieving precisesynchronization.

FIG. 53 shows the architecture according to the seventh embodiment. Withreference to FIG. 53, eNBs are divided into slave eNBs 5305, 5307, and5308 and a master eNB 5309, each of which separately functions as theMAC that performs scheduling. The UE establishes a physical link withthree slave eNBs (eNB(s)#1 (5305), eNB(s)#2 (5307), and eNB(s)#3(5308)), and the slave eNBs respectively establish master/slave eNBlinks 5314, 5314, and 5315 with the master eNB 5309. A MAC (MAC2) 5310of the master eNB configures discrete time frames for the slave eNBs5305, 5307, and 5308 and allocates the time frames to the slave eNBs.The slave eNBs 5305, 5307, and 5308 each schedule the data of a targeteNB in only the configured time frame over a radio physical channel.

FIG. 54 shows an example configuration of frames by scheduling performedby a MAC1 and a MAC2. The master eNB performs allocation to slave eNBson a time-frame-basis, and the slave eNBs perform schedulings (5411,5412, 5413, 5414, 5415) within radio frames (5401, 5403, 5405, 5407,5409). In consideration of precise synchronization not being achieved,guard times (G) (5402, 5404, 5406, 5408, 5410) are provided at frameboundaries and mapping is not performed during the guard times.

Here, the radio frames may be in units of subframes or may be in smallerunits. Note that the accuracy of the synchronization in eNBs needs to betaken into account and, if the unit of time frames is too small forsynchronization accuracy, the ratio of the guard times (G) increases,reducing radio use efficiency. The allocation time frame and guard timeaccordingly need to be provided in consideration of the synchronizationaccuracy of each eNB.

FIG. 55(A) shows an example sequence of a flow of establishingcommunication and transmitting data. The sequence includes Step ST5505being Service Request Procedure (Separate MAC) for first establishing abearer, Step ST5542 being DL Scheduling/Transmit Procedure that showsthe downlink data transmission/scheduling procedure, and Step ST5556being UL Scheduling/Transmit Procedure showing the uplink datatransmission/scheduling procedure.

FIG. 55(B) shows details of the service request procedure. ServiceRequest Procedure (Separate MAC) described here is based on the UETriggered Service Request Procedure described in Chapter 5.3.4.1 ofNon-Patent Document 11 (TS23.401). First, in Step ST5506, a NAS of theUE notifies an AS of Service Request, and then, in Step ST5508, the ASof the UE transmits RRC connection Request to an eNB#1. In Step ST5509,the eNB#1 that has received RRC connection Request data transmits thedata to a master eNB. As in UE triggered Service Request procedure, inStep ST5510 and Step ST5511, the master eNB that has received RRCconnection Request transmits RRC connection setup to the UE via theeNB#1. The UE that has received RRC connection setup performsconfiguration and, in Step ST5512 and Step ST5513, transmits RRCconnection Setup complete to the master eNB via the eNB#1. Thereafter,the procedure of UE triggered Service Request procedure is performed viathe eNB#1. In the procedure, the UE may directly communicate with themaster eNB, not via the slave eNB.

An eNB#3 establishes a link via the eNB#1, and then, activates StepST5534 being Radio Bearer Establishment procedure (a plurality of eNBs).Described here is a case in which an eNB#2 is added. First, in StepST5535 and Step ST5536, the information of the eNB#2 and its connectionrequest are transmitted to the UE via the eNB#1 in RRC connectionReconfiguration (eNB#2 Info). In Step ST5537 and Step ST5538, the UEthat has received RRC connection Reconfiguration (eNB#2 Info) transmitsRRC connection Reconfiguration complete to the master eNB via the eNB#2that has been specified.

A communication link is established through the process.

FIG. 55(C) shows details of the DL scheduling/transmit procedure. First,in Step ST5543, the master eNB performs time frame scheduling for twoeNBs. As in the first embodiment, the quality of a radio link andtraffic information should be taken into account in the configuration.The master eNB transmits the configured time frames to the slave eNBs inStep ST5544 and Step ST5545, and transmits the data to be transmitted tothe slave eNBs in Step ST5546 and Step ST5547. The slave eNBsrespectively schedule the transmission data within the selected timeframes in Step ST5548 and Step ST5549, and then transmit the schedulinginformation to the UE in Step ST5550 and Step ST5551 and transmit thedata to the UE in Step ST5552 and Step ST5553, and in Step ST5554 andStep ST5555.

FIG. 55(D) shows details of the UL scheduling/transmit procedure. First,as with DL, in Step ST5557, the master eNB performs time framescheduling for two eNBs. In Step ST5558 and Step ST5559, the master eNBtransmits the configured time frames to the slave eNBs. The slave eNBsrespectively schedule the transmission data within the selected timeframes in Step ST5560 and Step ST5561 and transmit the schedulinginformation to the UE in Step ST5562 and Step ST5566. The UE receivesthe scheduling information and, based on the scheduling information,transmits transmission data in Step ST5563 to Step ST5565, and StepST5567 to Step ST5569.

The seventh embodiment above enables the slave eNBs and the master eNBto perform scheduling with different accuracies. By properly configuringa guard time, scheduling can be performed to a plurality of cells in aunified manner even if precise synchronization accuracy cannot be kept.

Eighth Embodiment

When the UE performs communication using a plurality of eNBs (cells),communication with one cell may be performed if the communicationquality with another cell degrades. For example, if the communicationquality with an eNB (cell) that has established C-plane connectiondegrades, data communication with an eNB (cell) that has establishedonly U-plane connection can be performed.

In the case where the communication quality between the UE and theC-plane establishing eNB (cell) degrades, however, the RRC signaling forthe process of configuring/modifying (changing)/releasing a U-plane onlyestablishing eNB (cell) will not be notified the UE. For example, theC-plane establishing eNB (cell) will not notify the UE of ST3016 of FIG.30, ST3105 of FIG. 31, or the like disclosed in the second embodiment.

Thus, in the state where, for example, communication cannot be performeddue to the degraded communication quality between the UE and the C-planeestablishing eNB (cell), the communication with the U-plane establishingeNB (cell) cannot be disconnected, forcing the UE to continuouslymaintain the resources for the communication with the U-planeestablishing eNB (cell).

As described above, the UE cannot control the U-plane establishing eNB(cell), leading to a problem that, for example, data communicationcannot be performed normally or unnecessary resources are generated.

<Conventional RLF-Related Process>

There is a process related to a radio link failure (RLF) asspecifications for the degraded communication quality between a UE and acell (Non-Patent Document 1 (TS36.300 10.1.6), and Non-Patent Document 2(TS36.331 5.3.11)). The process related to an RLF will be referred to asan RLF-related process thereafter.

FIG. 56 is a diagram for describing the RLF-related process. The UE canbe categorized into four states; normal operation, first phase, secondphase, and RRC_Idle.

The UE performs monitoring of a radio link (RLM) for one cell with whichcommunication is performed.

The RLM is performed by, for example, evaluating the communicationquality of a PDCCH. The communication quality of the PDCCH not less thana predetermined threshold is referred to as in-sync, and thecommunication quality not greater than a predetermined threshold isreferred to as out-of-sync. The UE evaluates the reception quality of aCRS as the communication quality of a PDCCH.

The UE in the normal operation enters the first phase when detectingout-of-sync (radio problem detection) a predetermined number of times(N11) in a row.

The UE continuously performs RLM with one cell with which communicationis performed and, when detecting in-sync a predetermined number of times(N12) in a row in the first phase, returns to the normal operationstate. When not detecting in-sync the predetermined number of times(N12) in a row within a predetermined period (T11) from the radioproblem detection, the UE regards that an RLF has been detected and thenenters the second phase.

In the second phase, the UE stores RLF information and activates aprocess of reestablishing RRC connection (RRC connectionreestablishment). If AS security has not been activated, the UE performsa process of leaving from RRC connection (leaving RRC_Connected). The ASsecurity is the security for an RRC or U-plane.

In the process of leaving from RRC connection, the UE releases all theradio resources including releasing of the MAC, RLC, and PDCP of all theRBs, and then shifts to the RRC_Idle state.

To activate the RRC connection reestablishment process, the UE, forexample, stops all the RBs except for an SRB0, resets the MAC, releasesthe SCell, applies the predetermined (default) PHY configuration, andapplies the default MAC main configuration, to thereby perform a cellselection process.

When selecting a suitable cell in the cell selection process within apredetermined period (T12) from the detection of an RLF, the UE performsthe process of reestablishing RRC connection with the cell.

When it fails to select a suitable cell within the predetermined period(T12) from the detection of an RLF, the UE performs the process ofleaving from RRC connection (leaving RRC_Connected).

The conventional RLF-related process, however, has only thespecifications for one cell (primary cell).

In communication using a plurality of different eNBs (cells),accordingly, if the conventional RLF-related process is to be applied,the process cannot be applied because the information on only a singlecell is specified. For example, in the case where C-plane connection isestablished with one eNB (cell) and U-plane connection is establishedwith a plurality of eNBs (cells), if the communication quality with oneeNB (cell) deteriorates, the communication with another eNB (cell) canbe performed as long as the communication quality with the other eNB(cell) is good. If the conventional RLF-related process is applied inthe case where there is another communicable eNB (cell), the processdoes not operate normally because the communications with a plurality ofeNBs (cells) are not taken into account.

This embodiment will disclose the method of an RLF-related process whena UE performs communication using a plurality of different eNBs (cells).

<New RLF-Related Process>

A UE performs RLM for only a C-plane establishing eNB (cell). The UE mayperform or may not perform the RLM for a U-plane only establishing eNB(cell) and an RLF-related process, disclosed in a ninth embodimentdescribed below.

The UE performs a process of disconnecting connection with a U-planeonly establishing eNB (cell) in accordance with a C-plane connectionstate not in accordance with a U-plane connection status. Alternatively,the UE may perform the process of disconnecting connection with aU-plane only establishing eNB (cell) in accordance with the connectionstatus with the C-plane establishing eNB (cell), not in accordance withthe connection status of a U-plane only establishing eNB (cell).

<Processing Method of Disconnecting Connection with U-Plane OnlyEstablishing eNB (a)>

A specific example of the processing method of disconnecting connectionwith a U-plane only establishing eNB (cell) will be disclosed.

When activating the process of leaving from RRC connection in connectionwith the C-plane establishing eNB (cell), the UE disconnects theconnection with the U-plane only establishing eNB (cell). The UE maydisconnect the connection with the U-plane only establishing eNB (cell)not only in the activation of the process of leaving from RRC connectionbut also in every point of the process of leaving from RRC connection.

As the process of disconnecting the connection with the U-plane onlyestablishing eNB (cell), the UE performs the process of disconnectingall the U-plane connections in all the connected U-plane onlyestablishing eNBs (cells). The UE releases all the U-plane radioresources including releasing of the MAC, RLC, and PDCP of all theU-plane RBs in all the U-plane only establishing eNBs (cells). Forexample, the UE may end the process of synchronizing with the U-planeonly establishing eNB (cell) or may end monitoring the PDCCH or ePDCCHfor scheduling from the U-plane only establishing eNB.

Part (a) of FIG. 57 is a diagram for describing an RLF-related processaccording to this embodiment.

A UE in a normal operation state performs RLM on a C-plane establishingeNB (cell) and, when detecting out-of-sync (radio problem detection) apredetermined number of times (N21) in a row, enters the first phase.

In the first phase, the UE continuously performs RLM with the C-planeestablishing eNB (cell) and, when detecting in-sync a predeterminednumber of times (N22) in a row, returns the normal operation state. Whennot detecting in-sync the predetermined number of times (N22) in a rowwithin a predetermined period (T21) from the radio problem detection,the UE detects an RLF and enters the second phase. Whether the periodT21 is exceeded can be managed by, for example, a timer that measuresthe time from the radio problem detection.

In the second phase, the UE stores RLF information and activates the RRCconnection reestablishment process.

The UE may perform the process of leaving from RRC connection if the ASsecurity has not been activated.

In the process of leaving from RRC connection, the UE releases all theradio resources including releasing of the MAC, RLC, and PDCP of all theRBs in the C-plane establishing eNB (cell).

If there is U-plane connection between the UE and the C-planeestablishing eNB (cell) in this case, all the radio resources arereleased, including releasing of the MAC, RLC, and PDCP of all the RBsfor the U-plane connection.

The UE disconnects the connection with the U-plane only establishing eNB(cell) when activating the process of leaving from RRC connection in theconnection with the C-plane establishing eNB (cell). The UE maydisconnect the connection with the U-plane only establishing eNB (cell)not only in activating the process of leaving from RRC connection butalso in every point of the process of leaving from RRC connection.

<RRC Connection Reestablishment Process>

To activate the RRC connection reestablishment process, the UE stops allthe RBs except for an SRB0 of the C-plane establishing eNB (cell) and,for example, resets the MAC, releases the SCell, applies the default PHYconfiguration, and applies the MAC main configuration, to therebyperform a cell selection process. If there is U-plane connection betweenthe UE and the C-plane establishing eNB (cell), the UE also stops allthe RBs for the U-plane connection.

<Method of Processing U-Plane Only Establishing eNB>

Disclosed below are two methods of processing a U-plane onlyestablishing eNB (cell) by a UE in activating the RRC connectionreestablishment process.

(1) The UE causes all the U-plane RBs of all the U-plane onlyestablishing eNBs (cells) to perform normally. The UE does not stop theU-plane RB.

(2) The UE stops all the U-plane RBs of all the U-plane onlyestablishing eNBs (cells).

The process (1) can simplify, in the case where, for example, the sameU-plane only establishing eNB (cell) is configured after the RRCconnection reestablishment process, the process of configuring U-planeconnection in the U-plane only establishing eNB (cell). In addition,data communication with the U-plane only establishing eNB (cell) isperformed, reducing a data loss and a delay time.

The process (2) can cause the process for the RB in the U-plane onlyestablishing eNB (cell) to be identical to the process for the RB in theC-plane establishing eNB (cell), and thus, control by the UE can beunified among a plurality of eNBs (cells), leading to an effect ofsimplified control.

Disclosed below are two specific examples of the process for eachprotocol in the process (2).

(2-1) All or part of the PHY, MAC, RLC, and PDCP is reset.

(2-2) All of the PHY, MAC, RLC, and PDCP are not reset.

In the process (2-1), a (default) configuration predetermined in, forexample, specifications may be provided for all or part of the PHY, MAC,RLC, and PDCP for a U-plane only establishing eNB (cell), and thedefault configuration may be applied to the reset protocol. Thissimplifies control, reducing malfunctions irrespective whether RRCconnection reestablishment succeeds or fails.

The process (2-2) allows, in the case where, for example, the sameU-plane only establishing eNB (cell) is configured after the RRCconnection reestablishment process, the process of configuring U-planeconfiguration in the U-plane only establishing eNB (cell) to beperformed at an early stage.

In the case where carrier aggregation (CA) is configured in a U-planeonly establishing eNB (cell) in activating the RRC connectionreestablishment process, the UE may release an SCell of the CA.

<Cell Section Failure>

When it cannot select a suitable cell or cannot reestablish RRCconnection with a cell within a predetermined period (T22) from the RLFdetection, the UE performs the process of leaving from RRC connection(leaving RRC_Connected) described above. Whether the period T22 isexceeded can be managed by, for example, a timer that measures the timefrom the RLF detection.

The UE that has performed the process of leaving from RRC connectionshifts to the RRC_Idle state.

In the RRC_Idle state, the UE has no U-plane connection.

In any of the two methods in which a UE processes a U-plane onlyestablishing eNB (cell) in activating the RRC connection reestablishmentprocess, the UE may disconnect the connection with the U-plane onlyestablishing eNB (cell) when activating the process of leaving from RRCconnection in the connection with the C-plane establishing eNB (cell).

<Cell Selection Success>

When selecting a suitable cell in the cell selection process within apredetermined period (T22) from the RLF detection, the UE performs theRRC connection reestablishment process on the cell.

The UE performs C-plane connection with the cell by performing the RRCconnection reestablishment process. The cell serves as a C-planeestablishing eNB (cell). The eNB (cell) that newly establishes C-planeconnection is referred to as a new C-plane establishing eNB (cell).

The cell may be a C-plane establishing eNB (cell) (referred to as anlast connected C-plane establishing eNB (cell)) with which the selectedeNB (cell) has been connected before an RLF. The last connected C-planeestablishing eNB (cell) serves as a new C-plane establishing eNB (cell).This is effective in the case where, for example, the communicationquality between the UE and the last connected C-plane establishing eNB(cell) degrades momentarily.

The conventional method is employed in the case where U-plane connectionis established in a new C-plane establishing eNB (cell).

<Case in which New C-Plane Establishing eNB (Cell) is Last ConnectedC-Plane Establishing eNB (Cell)>

Disclosed below is a case in which the selected new C-plane establishingeNB (cell) is a last connected C-plane establishing eNB (cell).

<Same U-Plane Only Establishing eNB (Cell) is Connected as it Is>

The UE is continuously in connection with the connected U-plane onlyestablishing eNB (cell).

When the UE causes the U-plane RB of the U-plane only establishing eNB(cell) to operate normally in the RRC connection reestablishmentprocess, the UE is continuously in connection with the U-plane onlyestablishing eNB (cell) and operates normally.

When stopping the U-plane RB of the U-plane only establishing eNB (cell)in the RRC connection reestablishment process, the UE deactivates thestop and operates normally.

Disclosed below are three specific examples of the trigger fordeactivating the stop.

(1) When the UE selects a last connected C-plane establishing eNB(cell).

(2) When the UE receives an RRC connection reestablishment message froma new C-plane establishing eNB (cell) in the RRC connectionreestablishment process.

(3) When the UE receives an RRC connection reconfiguration message froma new C-plane establishing eNB (cell) after the RRC connectionreestablishment process.

The example (1) allows for the recognition that the UE has selected alast connected C-plane establishing eNB (cell), and accordingly, it canbe judged that the connection with a last connected U-plane onlyestablishing eNB (cell) is possible. Thus, at that point of time, theU-plane RB that has been stopped in the U-plane only establishing eNB(cell) may be returned to the normal operation. Compared with theexamples (2) and (3), the U-plane connection with the U-plane onlyestablishing eNB (cell) can be returned to the normal operation at anearly stage without signaling from a new C-plane establishing eNB(cell). When the UE receives an RRC connection reestablishment rejectmessage from the new C-plane establishing eNB (cell) in the RRCconnection reestablishment process, the UE may perform the process ofdisconnecting the connection with the U-plane only establishing eNB(cell) at that point of time.

The example (2) allows the UE to judge that it can reestablish RRCconnection with the new C-plane establishing eNB (cell) being a lastconnected C-plane establishing eNB (cell). Thus, the UE may return theU-plane RB that has been stopped in the U-plane only establishing eNB(cell) to the normal operation at that point of time. This simplifiesthe process of connecting with the U-plane only establishing eNB (cell),reducing malfunctions.

The example (3) allows the UE to judge the provision of a radio bearer.Thus, the UE may return the U-plane RB that has been stopped in theU-plane only establishing eNB (cell) to the normal operation at thatpoint of time. This allows the UE to perform the process of connectingwith a U-plane only establishing eNB (cell) as required, eliminatingunnecessary operations.

In the methods (2) and (3), the information indicating that the U-planeRB that has been stopped is returned to the normal operation may beprovided to be included in an RRC connection reestablishment message oran RRC connection reconfiguration message. Explicit signaling asdescribed above allows the UE to explicitly make judgment, reducingmalfunctions.

<Reconfiguring Same U-Plane Only Establishing eNB (Cell)>

The new C-plane establishing eNB (cell) may newly reconfigure, for theUE, the same U-plane only establishing eNB (cell) as the eNB with whichthe UE is connected in the connection with a last connected C-planeestablishing eNB (cell). This is enabled because the new C-planeestablishing eNB (cell) is the same as the last connected C-planeestablishing eNB (cell).

The new C-plane establishing eNB (cell) may configure the same U-planeonly establishing eNB (cell) for the UE in the RRC connectionreestablishment process. The new C-plane establishing eNB (cell) mayperform reconfiguration over radio resource config dedicated in the RRCconnection reestablishment message. This enables reconfiguration at anearly stage.

Alternatively, for the UE, the new C-plane establishing eNB (cell) mayperform an RRC connection reconfiguration after the RRC connectionreestablishment process and then perform the configuration for the sameU-plane only establishing eNB (cell). Reconfiguration may be performedover radio resource config dedicated in the RRC connectionreconfiguration message. This simplifies control because the sameprocess as that of the configuration of the normal U-plane onlyestablishing eNB (cell) can be used.

As described above, in the connection with the same U-plane onlyestablishing eNB (cell) as that connected in the connection with thelast connected C-plane establishing eNB (cell), the UE needs not tonotify the MME of the information about the connection with the U-planeonly establishing eNB (cell). This is because the MME originallyperforms management while the target UE and the U-plane onlyestablishing eNB (cell) are being connected to each other, requiring nochange. In other words, the configuration of the DRB and/or the S1bearer needs not to be changed.

The MME needs no notification, which reduces an amount of signaling as asystem. The U-plane only establishing eNB (cell) can be kept to beconnected, simplifying control of the UE and the NW side.

<Configuring Different U-Plane Only Establishing eNB (Cell)>

The new C-plane establishing eNB (cell) may newly configure, for the UE,a U-plane only establishing eNB (cell) different from the eNB with whichthe UE connected in the connection with the last connected C-planeestablishing eNB (cell).

In the configuration of a different U-plane only establishing eNB(cell), the MME may configure the E-RAB of each eNB.

The selection and determination of a U-plane only establishing eNB(cell) may be performed by the new C-plane establishing eNB (cell) orthe MME.

The case in which the selection and determination are performed by thenew C-plane establishing eNB (cell) will be disclosed.

After the RRC connection reestablishment process, the new C-planeestablishing eNB (cell) selects and determines a U-plane onlyestablishing eNB (cell), and transmits a U-plane establishment requestmessage to the MME. The MME that has received the message determines theE-RAB configuration of each eNB (cell) to configure/modify the E-RAB foreach eNB (cell).

The method of the third modification of the second embodiment isapplicable to the processes from the processes described above to theprocess of configuring a U-plane only establishing eNB (cell).

For example, the sequence shown in FIG. 38, disclosed in the thirdmodification of the second embodiment, may be applied. The sequencestarting from ST3802 may be applied.

In configuring a different U-plane only establishing eNB (cell), theconnection with the last connected U-plane only establishing eNB (cell)is disconnected. The method disclosed in the third modification of thesecond embodiment is applicable to this specific example.

For example, the sequence shown in FIG. 39 may be applied. The sequencestarting from ST3902 may be applied.

Consequently, the connection of the last connected U-plane onlyestablishing eNB (cell) with the UE and the NW side can be reliablydisconnected, reducing use of unnecessary resources.

Disclosed below is a case in which the selection and determination of aU-plane only establishing eNB (cell) are performed by the MME.

After the RRC connection reestablishment process, a new C-planeestablishing eNB (cell) transmits a U-plane establishment requestmessage to the MME. Unlike the message disclosed in ST3803 of FIG. 38,the U-plane establishment request message requests the MME to start fromthe selection and determination of a U-plane only establishing eNB(cell). This request message may include the identifier of a target UEand the identifier of the own eNB (cell) (new C-plane establishing eNB(cell)). The MME that has received the request message selects anddetermines a U-plane only establishing eNB (cell) and determines theE-RAB configuration of each eNB (cell), to thereby configure/modify theE-RAB for each eNB (cell).

The method disclosed in the second embodiment is applicable to theprocesses from the above-mentioned process to the process of configuringa U-plane only establishing eNB (cell). For example, the sequence ofFIG. 30 is applicable. The sequence starting from ST3009 is applicable.

In configuring a different U-plane only establishing eNB (cell), theconnection with the last connected U-plane only establishing eNB (cell)is disconnected. The method disclosed in the second embodiment is alsoapplicable to the specific example. For example, the sequence shown inFIG. 31 may be applied. The sequence starting from ST3101 can beapplied.

Consequently, the connection of the last connected U-plane onlyestablishing eNB (cell) with the UE and the NW side can be reliablydisconnected, reducing use of unnecessary resources.

When the UE stops a U-plane RB with the U-plane only establishing eNB(cell) in the RLF-related process, the U-plane only establishing eNB(cell) may buffer the U-plane data during the stop. When the UE isconnected again with the same U-plane only establishing eNB (cell), thebuffered data may also be communicated. This allows for communicationwithout loss of data also in the case where the U-plane RB is stopped.

When the connection with the last connected U-plane only establishingeNB (cell) is disconnected to establish a connection with a new U-planeonly establishing eNB (cell), the timing of the process performedbetween the UE and each U-plane only establishing eNB (cell) may differfrom the timing of switching a bearer path between the UE and the S-GW.In such a case, the method disclosed in the second embodiment may beapplied. The method in the second embodiment may be applied, whichsolves the problem that it is unclear how downlink user data,transmitted to the U-eNB between the process of disconnecting theconnection with the U-eNB by the UE and the process ofreleasing/modifying the S1 bearer path by the S-GW, is handled. Thisreduces malfunctions as a system.

For example, in the case where the forwarding method among the methodsdisclosed in the second embodiment is used when the last connectedU-plane only establishing eNB (cell) buffers the U-plane data with theUE with which the eNB is connected, the processes from ST3302 to ST3304,disclosed with reference to FIG. 33, may be performed by the new U-planeonly establishing eNB (cell) and the last connected U-plane onlyestablishing eNB (cell). The processes from ST3302 to ST3304 by theC-eNB may be applied to the new U-plane only establishing eNB, and theprocesses from ST3302 to ST3304 by the U-eNB may be applied to the lastconnected U-plane only establishing eNB (cell). This allows a differentU-plane only establishing eNB (cell) to be configured and connectedwithout any loss of downlink data.

The MME may notify the new U-plane only establishing eNB (cell) of aforwarding configuration command message for the last connected U-planeonly establishing eNB (cell). The message may include, for example, theidentifier of the last connected U-plane only establishing eNB (cell)and the identifier of the UE being a communication target. This allowsthe new U-plane only establishing eNB (cell) to request the U-plane dataforwarding configuration to the last connected U-plane only establishingeNB (cell), enabling the forwarding process.

Contrastingly, the MME may notify the last connected U-plane onlyestablishing eNB (cell) of the forwarding configuration command messagefor the new U-plane only establishing eNB (cell). The message mayinclude, for example, the identifier of the new U-plane onlyestablishing eNB (cell) and the identifier of the UE being acommunication target. An S1 interface may be used to notify the message.This allows the last connected U-plane only establishing eNB (cell) torequest the new U-plane only establishing eNB (cell) to configureU-plane data forwarding, enabling the forwarding process.

In the case where the C-plane establishing eNB (cell) recognizes theidentifiers of the new U-plane only establishing eNB (cell) and the lastconnected U-plane only establishing eNB (cell), the C-plane establishingeNB (cell) may notify the new or last connected U-plane onlyestablishing eNB (cell) of the forwarding configuration command message.The interface between eNBs, such as X2, may be used for the message.This achieves the effects similar to the above. In this case, signalingwith the MME is not required.

Disclosed below is another method in which a new C-plane establishingeNB (cell) newly configures, for the UE, a U-plane only establishing eNB(cell) different from the eNB with which the UE connected in theconnection with the last connected C-plane establishing eNB (cell).

After the RRC connection reestablishment process, the UE or the NW mayissue a U-plane connection request when the U-plane connection isrequired. A service request may be issued as the U-plane connectionrequest.

The MME or the new C-plane establishing eNB (cell) judges (selects anddetermines) whether configuring_a U-plane only establishing eNB (cell)is necessary. When judgment is made by the new C-plane establishing eNB(cell), the new C-plane establishing eNB (cell) may transmit the U-planeestablishment request message to the MME subsequent to the U-planeconnection request.

The method disclosed above is applicable to the subsequent processes.

Although the method of newly configuring, for the UE, a U-plane onlyestablishing eNB (cell) different from the eNB with which the UEconnected in the connection with the last connected C-plane establishingeNB (cell) has been described above, a part of the last connectedU-plane only establishing eNBs (cells) may be included in the cells tobe configured. The method disclosed above is applicable.

Consequently, the new C-plane establishing eNB (cell) can newlyconfigure, for the UE, a U-plane only establishing eNB (cell) differentfrom the eNB with which the UE connected in the connection with the lastconnected C-plane establishing eNB (cell). The U-plane only establishingeNB (cell) according to the status of a new connection between the UEand the new C-plane establishing eNB (cell) can be selected andconfigured, preventing a drop in data rate in the selection of a newC-plane establishing eNB (cell).

Although the method above has disclosed that the new C-planeestablishing eNB (cell) or the MME selects and determines a U-plane onlyestablishing eNB (cell), the priority may be provided in the selectionand determination. The last connected U-plane only establishing eNB(cell) connected with a target UE may be preferentially selected anddetermined.

Consequently, the cell has the same configuration as that of the lastconnected U-plane only establishing eNB (cell), eliminating theconfiguration parameter when the configuration parameter required toreconfigure the U-plane only establishing eNB (cell) is the same. Onlythe information for requesting reconnection may be used as the signalingof the reconfiguration from the MME to each eNB (cell), and/or from theU-plane only establishing eNB (cell) to the C-plane only establishingeNB (cell), and/or from the C-plane only establishing eNB (cell) to theUE. This reduces an amount of signaling as a system.

Specific examples of the information for requesting reconnection mayinclude the information indicative of a request for connection, theidentifier of a target UE, the identifier of a target U-plane onlyestablishing eNB (cell), the identifier of a C-plane only establishingeNB (cell), and an E-RAB number.

A U-plane only establishing eNB (cell) that can be configured of a newC-plane establishing eNB (cell) may be selected and determined inanother method in selection and determination. A U-plane onlyestablishing eNB (cell) reliably connectable with the UE can beconfigured.

A timer T32 or T33 of the last connected C-plane establishing eNB (cell)in the RLF-related process by the C-plane establishing eNB (cell),described below, may be stopped in the RRC connection reestablishmentprocess by the UE. As a specific example, the timer may be stopped uponreceipt of RRC connection reestablishment request or upon receipt of RRCconnection reestablishment complete. Consequently, the process ofreleasing the connection of the NW side with the U-plane onlyestablishing eNB (cell), performed upon expiration of the timer, is notperformed. This prevents a situation in which RRC connection isreestablished between the UE and the last connected C-plane establishingeNB (cell) but the C-plane and U-plane connections are disconnectedbetween the UE and the last connected C-plane establishing eNB (cell).

A value obtained by taking into account a period in which the UE mayperform the RRC connection reestablishment process may be used as thepredetermined period.

<Case in which New C-Plane Establishing eNB (Cell) Differs from LastConnected C-Plane Establishing eNB (Cell)>

Disclosed below is a case in which the new C-plane establishing eNB(cell) selected by the UE differs from the last connected C-planeestablishing eNB (cell).

A U-plane only establishing eNB (cell) is newly configured. In thiscase, the MME may configure the E-RAB of each eNB (cell).

The U-plane only establishing eNB (cell) may be selected and determinedby a new C-plane establishing eNB (cell) or the MME.

The method, in which a new C-plane establishing eNB (cell) newlyconfigures, for the UE, a U-plane only establishing eNB (cell) differentfrom the eNB with which the UE connected in the connection with the lastconnected C-plane establishing eNB (cell), may be applied as thesemethods.

Consequently, effects similar to those described above are achieved alsoin the case where the UE selects a different C-plane establishing eNB(cell) in cell selection.

<Selecting and Determining Same U-Plane Only Establishing eNB (Cell)>

The UE may notify the new C-plane establishing eNB (cell) of theinformation of the last connected U-plane only establishing eNB (cell).

As the notification method, for example, the information may be notifiedin the process of reestablishing RRC connection with the new C-planeestablishing eNB (cell) selected by the UE. The information may benotified by being included in the RRC connection reestablishment requestor RRC connection reestablishment complete message in the RRC connectionreestablishment process.

Examples of the information of the last connected U-plane onlyestablishing eNB (cell) include, for example, the cell identifier andthe cell identifier identifiable by the MME. Or, the information mayinclude the communication quality between the UE and each U-plane onlyestablishing eNB (cell).

The new C-plane establishing eNB (cell), which has received theinformation of the last connected U-plane only establishing eNB (cell)from the UE, can recognize a U-plane only establishing eNB (cell) withwhich the UE has been connected.

This allows for the application of the method in the case where the UEselects a last connected C-plane establishing eNB (cell) as a newC-plane establishing eNB (cell).

The new C-plane establishing eNB (cell) may perform selection anddetermination of a new U-plane only establishing eNB (cell) inconsideration of a U-plane only establishing eNB (cell) with which theUE has been connected. The last connected U-plane only establishing eNB(cell) may be preferentially selected and determined.

If there is no change in the U-plane only establishing eNB (cell)selected and determined in the new C-plane establishing eNB (cell), theMME may be not notified of the selected and determined U-plane onlyestablishing eNB (cell).

The new C-plane establishing eNB (cell) may notify the UE that the eNBis connected with the same U-plane only establishing eNB (cell).

The UE that has received the notification may perform transmission andreception with the U-plane only establishing eNB (cell) in the normaloperation or may deactivate the stopped RB of the U-plane onlyestablishing eNB (cell) and return to the normal operation to performtransmission and reception.

<RLF-Related Process by C-Plane Establishing eNB (Cell)>

The RLF-related process by the C-plane establishing eNB (cell) will bedisclosed.

The C-plane establishing eNB (cell) evaluates the status of theconnection with a target UE and, when judging that the connection has aproblem, detects a radio problem with the UE.

The following six specific examples of an event by which it is judgedthat the connection has a problem will be disclosed as to the method ofevaluating the connection with a target UE by the C-plane establishingeNB (cell).

(1) Ack/Nack is undelivered to the PDSCH.

(2) The PUSCH is undelivered.

(3) The SRS is undelivered.

(4) The PUCCH is undelivered.

(5) The periodic CQI or periodic CSI is undelivered.

(6) Combination of (1) to (5).

In (1), the C-plane establishing eNB (cell) judges that when it cannotreceive Ack/Nack transmitted from the UE for downlink communication, theconnection has a problem and detects a radio problem. The C-planeestablishing eNB (cell) may judge as described above in the case whereit cannot receive Ack/Nack N31 times in a row.

In (2) and (3), the C-plane establishing eNB (cell) judges that when itcannot receive the PUSCH or sounding reference signal (SRS) transmittedfrom the UE for uplink communication, the connection has a problem anddetects a radio problem. The C-plane establishing eNB (cell) may judgeas described above in the case where it cannot receive the PUSCH or SRSN31 times in a row.

In (4), the C-plane establishing eNB (cell) judges that when it cannotreceive the PUCCH transmitted from the UE for uplink communication, theconnection has a problem and detects a radio problem. The C-planeestablishing eNB (cell) may judge as described above in the case whereit cannot receive the PUCCH N31 times in a row.

In (5), the C-plane establishing eNB (cell) judges that when it cannotreceive the periodic CQI or periodic CSI transmitted from the UE foruplink communication, the connection has a problem and detects a radioproblem. The C-plane establishing eNB (cell) may judge as describedabove in the case where it cannot receive the periodic CQI or periodicCSI N31 times in a row.

In (1) to (6), the C-plane establishing eNB (cell) may detect a radioproblem when communication quality has degraded, not when undelivery hasoccurred. A predetermined threshold may be provided in the communicationquality for detecting a radio problem. The C-plane establishing eNB(cell) may evaluate the reception quality of the reference signal (RS)or the signal equivalent to the RS, transmitted from the UE togetherwith each channel or signal, and when the reception quality falls belowthe predetermined threshold, judge that the communication quality hasdegraded to determine that radio problem has been detected.

Consequently, the C-plane establishing eNB (cell) can also evaluate thestatus of the connection with a target UE and, when judging that theconnection has a problem, determine that a radio problem has beendetected between the UE and itself.

The number of successive receptions, serving as a threshold, is N31times in the specific items (1) to (5), which may differ per item. Thisenables the adjustment according to the communication environment.

After detecting a radio problem with a target UE, the C-planeestablishing eNB (cell) performs management by time as in theRLF-related process by the UE.

In the case where the C-plane establishing eNB (cell) detects a radioproblem, the C-plane establishing eNB (cell) continuously evaluates thestatus of the connection with a target UE and, when each signal in (1)to (6) above has arrived (has been delivered) N31 times in a row,returns to the normal operation state. When the delivery has not beendetected the predetermined number of times (N31 times) in a row within apredetermined period (T31) from the radio problem detection, the RLF isdetected. Whether the period T31 has been exceeded can be managed using,for example, the timer that measures a time from the radio problemdetection.

When an RLF is detected, if an RRC connection reestablishment requestmessage is received from the UE within a predetermined period (T32), theprocess of reestablishing RRC connection with the UE is performed.

If not receiving an RRC connection reestablishment request message fromthe UE within the predetermined period (T32), the process ofdisconnecting the connection between the UE and the C-plane establishingeNB (cell) is performed. Whether the period T32 has been exceeded can bemanaged using, for example, a timer that measures a time from the RLFdetection.

If there is a connection between the UE and the U-plane onlyestablishing eNB (cell) in this case, the process of disconnecting theconnection with the U-plane only establishing eNB (cell) is performed.

As the process of disconnecting connection, a resource for theconnection of the C-plane establishing eNB (cell) and the U-plane onlyestablishing eNB (cell) with the UE is released or the information forthe connection is deleted.

Examples of the resource and information for the connection with the UEinclude the resource and information for configuring an RB/S1 bearer,which is, for example, a UE context.

The C-plane establishing eNB (cell), which has judged to perform theprocess of disconnecting the connection with the UE, releases the RB/S1with the UE and deletes the information for connection. The resource(RB/S1) for C-plane and U-plane connections that is configured betweenthe UE and the C-plane establishing eNB (cell) is released, and deletionof the information for connection is performed.

After the completion of the processes above, the C-plane establishingeNB (cell) may notify the MME of an E-RAB release complete message.

The C-plane establishing eNB (cell) may release the radio resource(DRB/S1) for U-plane connection with the UE and delete the informationfor connection, in response to an E-RAB release request from the MME. Inthis case, the MME may notify the U-plane establishing eNB of the E-RABrelease request message.

The C-plane establishing eNB (cell) may release the RB/S1 bearer betweenthe UE and itself or delete the information for connection in responseto an E-RAB release request from the MME. In this case, the MME maynotify the U-plane establishing eNB of an E-RAB release request messageincluding the information indicating that the release of a bearer istargeted for all the RB/S1 bearers.

Disclosed below is a specific example of the method of releasing anRB/S1 bearer between the U-plane only establishing eNB (cell) and the UEand deleting the information for connection.

The C-plane establishing eNB (cell), which has judged to perform theprocess of disconnecting the connection with the UE, notifies the MME ofa U-plane connection release request message for the UE.

The U-plane connection release request message may include theidentifier of a target UE. If the C-plane establishing eNB recognizesthe U-plane only establishing eNB connected with the UE, the message mayinclude the identifier of the U-plane only establishing eNB.Alternatively, the reason for performing the process of disconnectingconnection may be notified. The notification of the information onreason allows the MME to judge a process to be performed.

The MME that has received the message notifies the U-plane onlyestablishing eNB established for the UE of a connection release requestmessage for requesting the release of all the RB/S1 bearers with the UEand the deletion of the information for connection. An E-RAB releaserequest message may be applied as the connection release requestmessage. The connection release request message may include theidentifier of a target UE.

The MME requests the S-GW to release the configuration for the U-planeonly establishing eNB established for the UE. ST3110 to ST3112 disclosedin the second embodiment with reference to FIG. 31 may be applied asthis method. The S-GW that has received a modify bearer request, whichis applied as the request message, releases the configuration for theU-plane only establishing eNB connected with a target UE, such as thepath configuration of the S1 bearer. After the release, the S-GW maynotify the MME of a release complete message. A modify bearer responsemay be applied.

The U-plane only establishing eNB (cell) that has received a connectionrelease request message uses the notified identifier of the UE torelease the radio resource (DRB/S1) for U-plane connection, configuredbetween the UE and itself, and deletes the information for connection.

After completing these processes, the U-plane only establishing eNB(cell) may notify the MME of a U-plane connection release completemessage. An E-RAB release complete message may be applied as the U-planeconnection release complete message. The MME can surely recognize thateach U-plane only establishing eNB has released the resource for U-planeconnection of the target UE and deleted the information.

The methods of releasing an eNB, disclosed in the first embodiment, thesecond embodiment, and the third modification of the second embodiment,are applicable to the processes of disconnecting connection. However,among the processes, the connection between the UE and the C-planeestablishing eNB cannot be performed, and thus, the process of signalingbetween the UE and the eNB having RRC connection or other process is notperformed.

For example, in the application of the method disclosed in the firstembodiment, ST2302 of the sequence in FIG. 23 may be applied. In thiscase, ST2310 is not performed.

For example, in the application of the method disclosed in the secondembodiment, for example, the processes from ST3101 to ST3112 of thesequence in FIG. 31 may be applied. In this case, ST3105, ST3106, andST3107 are not performed. Further, ST3104 and ST3108 relate to thesignaling performed between the UE and the U-plane only establishingeNB, and thus, those processes may be skipped.

For example, in the application of the method disclosed in the thirdmodification of the second embodiment, for example, the processes fromST3902 to ST3112 of the sequence in FIG. 39 may be applied. Also in thiscase, ST3105, ST3106, ST3107, ST3104, and ST3108 in ST3114 may beskipped.

Disclosed below is another specific example of the method of releasingthe RB/S1 bearer between the U-plane only establishing eNB (cell) andthe UE and deleting the information for connection.

The C-plane establishing eNB (cell), which has judged to perform theprocess of disconnecting the connection with the UE, may directly notifythe U-plane only establishing eNB established for the UE of a connectionrelease request message. An X2 interface or other interface may be used.

The connection release request signal may include the identifier foridentifying a target UE.

The U-plane only establishing eNB (cell) that has received theconnection release request signal releases the radio resources (DRB/S1)for U-plane connection configured between the notified UE and itself anddeletes the information for connection. After completing theseprocesses, the U-plane only establishing eNB (cell) notifies the MME ofa U-plane connection release complete message. An E-RAB release completemessage may be applied as the U-plane connection release completemessage.

The MME that has received the U-plane connection release completemessage requests the S-GW to release the configuration for the U-planeonly establishing eNB established for the UE. The method described abovemay be applied as this method. This allows the S-GW to release theconfiguration.

This method enables the release of the resource for the connectionsbetween the C-plane establishing eNB (cell) and the UE and between theU-plane only establishing eNB (cell) and the UE and the deletion of theinformation for connection.

The NW side can release an unnecessary resource and delete information,and thus, the NW-side node needs not to continuously maintain anunnecessary resource or store unnecessary information, improvingresource use efficiency.

The release process is performed also by the NW side, preventing thedisagreement of the state between the UE and the NW side to the extentpossible. This accordingly reduces malfunctions as a system.

Although T31 and T32 are provided as predetermined periods in the methodabove, judgment may be made within one period in another example.

If delivery has not been detected a predetermined number of times (N32times) in a row within a predetermined period (T33) from the C-planeestablishing eNB (cell) detecting a radio problem, or if an RRCconnection reestablishment request message has not been unsuccessfullyreceived within the predetermined period, the process of disconnectingthe connections between the UE and the C-plane establishing eNB (cell)and between the UE and the U-plane only establishing eNB (cell) isperformed.

If delivery has been detected the predetermined number of times (N32times) in a row within the predetermined period (T33) or if an RRCconnection reestablishment request message has been successfullyreceived, the method described above may be applied. Whether the periodT33 is exceeded can be managed by, for example, a timer that measuresthe time from the radio problem detection.

Providing one period for configuration simplifies control.

FIG. 58 shows an example sequence of an RLF-related process according toan eighth embodiment, which also shows an RLF-related process by the UEand an RLF-related process by the C-plane establishing cell.

In ST5801, the UE that has shifted to the RRC_Connected state starts anRLM with the C-eNB. In ST5802, the UE judges whether out-of-sync hasoccurred N21 times in a row in the connection with the C-eNB. Ifout-of-sync has occurred N21 times in a row, the UE detects a radioproblem (ST5803) to shift to the first phase. If out-of-sync has notoccurred N21 times in a row, the UE performs RLM and again performsST5802. In ST5804, the UE that has detected a radio problem in ST5803starts a timer T21. The UE continuously performs RLM in the first phase.In ST5805, the UE judges whether in-sync has occurred N22 times in arow. If in-sync has occurred N22 times in a row, the UE returns to thenormal operation to continuously perform RLM, and then performs ST5802.If in-sync has not occurred N22 times in a row, in ST5806, the UE judgeswhether the timer T21 has expired. If the timer T21 has not expired, theUE continuously performs RLM and then performs ST5805. If the timer hasexpired, the UE detects an RLF in ST5807. The UE that has detected anRLF in ST5807 enters a second phase and, in ST5808, stops the timer T21and starts a timer T22. In the example shown in FIG. 58, the UE does notstop the RB with the U-plane only establishing cell (U-eNB) and causesRB to be operated normally in the second phase. In the second phase, theUE activates the cell selection process to perform cell search (ST5809).In ST5810, the UE judges whether it has succeeded in cell search and, ifit has failed in cell selection, judges whether the timer T22 hasexpired in ST5811. If the timer T22 has not expired, the UE continuouslyperforms cell search in ST5809. If the timer T22 has expired in ST5811,the UE performs the process of leaving from RRC connection in ST5812 anddisconnects the connection between the UE and the U-eNB in ST5813. Byperforming the process of leaving from RRC connection, the UE shifts toRRC_Idle in 3001. In RRC_Idle of 3001, the connection between the UE andthe U-eNB is disconnected, and thus, there is no U-eNB connected inRRC_Idle.

This prevents a problem that when the UE shifts to the RRC_Idle stateduring communication using a plurality of eNBs, the UE unnecessarilymaintains radio resources for U-plane connection, improving radioresource use efficiency.

If the UE has succeeded in cell selection in ST5810, the UE stops thetimer T22 in ST5814 and judges whether the selected cell is a lastconnected C-eNB in ST5815. If the selected cell is not a last connectedC-eNB, the UE performs the process [B]. A specific example of theprocess [B] will be disclosed below with reference to FIG. 61. If theselected cell is a last connected C-eNB, the UE performs a series ofprocesses of reestablishing RRC connection indicated by ST5816 betweenthe selected last connected C-eNB and itself. The UE notifies the lastconnected C-eNB of an RRC connection reestablishment request message inST5817, and the last connected C-eNB notifies the UE of an RRCconnection reestablishment message in ST5821. The UE that has receivedthe RRC connection reestablishment message performs the RRC connectionreestablishment process between the last connected C-eNB and itself. InST5823, the UE, which has completed the process of reestablishing RRCconnection with the last connected C-eNB, notifies the last connectedC-eNB of an RRC connection reestablishment complete message. The RRCconnection reestablishment process reconfigures a radio bearer 1 (3003)between the UE and the last connected C-eNB and an S1 bearer 1 (3004)between the last connected C-eNB and the S-GW. The connection betweenthe UE and the U-eNB is normally operated in the second phase, and thus,the radio bearer 2 (DRB) (3027) is continuously configured between theUE and the U-eNB (last connected U-eNB) and the S1 bearer 2 (3028)between the U-eNB and the S-GW. This allows the U-plane data to becommunicated between the UE and the S-GW via the last connected C-eNB inST3005 and ST3006 and the U-plane data to be communicated between the UEand the S-GW via the last connected U-eNB in ST3032 and ST3033. Thisallows the UE to perform communication using the last connected C-eNBand the last connected U-eNB.

FIG. 58 shows a case in which the UE does not stop an RB with theU-plane only establishing cell (U-eNB) in the second phase and causes RBto be operated normally. If the UE stops an RB with the U-plane onlyestablishing cell (U-eNB) in the second phase, the process of stoppingan RB with the U-eNB may be added after ST5808 and before ST5809.Further, if the last connected C-eNB is selected in ST5815, the lastconnected C-eNB may include the information (such as U-eNB reactivationinformation) indicating that the UE returns the U-plane RB that has beenstopped to the normal operation in the RRC connection reestablishmentmessage (ST5812) during the RRC connection reestablishment process, andthen notify the UE of the information. Alternatively, the last connectedC-eNB may include the U-eNB reactivation information in an RRCconnection reconfiguration message and notify the UE of the informationafter the RRC connection reestablishment process. The UE, which hasreceived the U-eNB reactivation information, reactivates the RB of theU-eNB that has been stopped and then returns to the normal operation. Asa result, the radio bearer 2 (DRB) (3027) is configured between the UEand the U-eNB (last connected U-eNB) and the S1 bearer 2 (3028) isconfigured between the U-eNB and the S-GW, and the U-plane data can becommunicated between the UE and the S-GW via the last connected U-eNB.The UE can accordingly perform communication using the last connectedC-eNB and the last connected U-eNB.

The RLF-related process by the C-eNB will now be described.

In ST5826, the C-eNB that is in C-plane connection with the UE startsRLM between the UE and itself. In ST5827, the C-eNB judges whether anuplink signal or channel has been undelivered N31 times in a row in theconnection with the UE. The uplink signal may be, for example, aperiodic CQI. If a periodic CQI has been undelivered N31 times in a row,the C-eNB detects a radio problem (ST5828). If a periodic CQI has notbeen undelivered N31 times in a row, the C-eNB performs RLM and performsST5827 again. In ST5829, the C-eNB that has detected a radio problem inST5828 starts the timer T31 and continuously performs RLM. In ST5830,the C-cNB judges whether it has successfully received a periodic CQI N32times in a row. If having successfully received a periodic CQI N32 timesin a row, the C-eNB returns to the normal operation to continuouslyperform RLM and performs ST5827. If having failed in receiving aperiodic CQI N32 times in a row, in ST5831, the C-eNB judges whether thetimer T31 has expired. If the timer T31 has not expired, the C-eNBcontinuously performs RLM and performs ST5830. If the timer has expired,the C-eNB detects an RLF in ST5832. In ST5833, the C-eNB that hasreceived an RLF in ST5832 stops the timer T31 and starts the timer T32.In ST5818, the C-eNB judges to have received the RRC connectionreestablishment request from the UE. If it has received the request, theC-eNB stops the timer T32 in ST5819. The C-eNB judges whether to selectthe last connected U-eNB in ST5820 and, if it selects the last connectedU-eNB, moves to the processes of ST5821 and ST5823. If it does notselect the last connected U-eNB in ST5820, the C-eNB notifies the UE ofan RRC connection reestablishment message in ST5822. The UE that hasreceived the RRC connection reestablishment message performs the processof reestablishing RRC connection with the last connected C-eNB. InST5824, the UE, which has completed the process of reestablishing theRRC connection with the last connected C-eNB, notifies the lastconnected C-eNB of an RRC connection reestablishment complete message.The last connected C-eNB that has received the RRC connectionreestablishment complete message performs the process [A]. A specificexample of the process [A] will be disclosed with reference to FIG. 59or FIG. 60 below.

If not receiving the RRC connection reestablishment request from the UEin ST5818, the C-eNB judges whether the timer T32 has expired in ST5825.If the timer T32 has not expired, the C-eNB returns to ST5818 and thencontinuously performs judgment. The last connected C-eNB, which hasjudged that the timer T32 had expired in ST5825, activates the processof disconnecting the connection with the UE. As a result of the processof disconnecting connection being activated, the process ofdisconnecting the connection between the UE and the last connected C-eNBand the process of disconnecting the connection between the UE and theU-eNB are performed. The processes are shown in [C] and thereafter. Aspecific example of the process [C] will be disclosed with reference toFIG. 62 below.

FIG. 59 shows an example sequence of the process [A] in FIG. 58.Disclosed below is a case in which the last connected C-eNB selects anddetermines a new U-plane establishing eNB (cell) (new U-eNB).

If not selecting the last connected U-eNB in ST5820 of FIG. 58, the lastconnected C-eNB performs the RRC connection establishment process forthe UE and then moves to the process [A]. The last connected C-eNBperforms the RRC connection establishment process on the UE, so that asshown in FIG. 59, the radio bearer 1 (3003) is reconfigured between theUE and the last connected C-eNB and the S1 bearer 1 (3004) isreconfigured between the last connected C-eNB and the S-GW. This allowsthe U-plane data to be communicated between the UE and the S-GW via thelast connected C-eNB in ST3005 and ST3006.

After the RRC connection reestablishment process, the last connectedC-eNB selects and determines a new U-eNB and performs the process forthe U-plane connection with the new U-eNB. The processes disclosed withreference to ST3802 to ST3036 of FIG. 38 are applied as a series of theprocesses. As a result, the radio bearer 2 (DRB) is configured betweenthe UE and the new U-eNB and the S1 bearer 2 is configured between thenew U-eNB and the S-GW, allowing the U-plane data to be communicatedbetween the UE and the S-GW via the new U-eNB.

Consequently, the UE can perform communication using the last connectedC-eNB and the new U-eNB.

The method disclosed with reference to FIG. 39 in the third modificationof the second embodiment may be applied to the process of releasing alast connected U-eNB. ST3902 to ST3115 of FIG. 39 can be applied. TheMME configures the new U-eNB in ST3010, and can thus release the lastconnected U-eNB. In this case, ST3011 to ST3115 may be applied. Thesequence of configuring a new U-eNB and the sequence of releasing a lastconnected U-eNB may be performed continuously or in parallel.

FIG. 60 shows another example sequence of the process [A] in FIG. 58.Disclosed below is a case in which the MME selects and determines a newU-plane establishing eNB (cell) (new U-eNB).

If the last connected U-eNB is not selected in ST5820 of FIG. 58, thelast connected C-eNB performs the RRC connection establishment processon the UE and then moves to the process [A]. The last connected C-eNBperforms the RRC connection establishment process on the UE,reconfiguring the radio bearer 1 (3003) between the UE and the lastconnected C-eNB and the S1 bearer 1 (3004) between the last connectedC-eNB and the S-GW in 3003 and 3004, respectively, as shown in FIG. 60.This allows the U-plane data to be communicated between the UE and theS-GW via the last connected C-eNB in ST3005 and ST3006.

After the RRC connection reestablishment process, in ST6001, the lastconnected C-eNB notifies the MME of a U-plane establishment requestmessage requesting to start from the selection and determination of aU-plane only establishing eNB (cell). The MME that has received theU-plane establishment request message selects and determines a U-planeonly establishing eNB (cell) and determines the E-RAB configuration ofeach of the eNBs (cells), to thereby configure/modify the E-RAB for eachof the eNBs (cells). The processes disclosed with reference to ST3009 toST3036 of FIG. 30 are applied as the processes from these processes tothe process of configuring a U-plane only establishing eNB (cell). As aresult, the radio bearer 2 (DRB) is configured between the UE and thenew U-eNB and the S1 bearer 2 is configured between the new U-eNB andthe S-GW, allowing the U-plane data to be communicated between the UEand the S-GW via a new U-eNB.

Consequently, the UE can perform communication using the last connectedC-eNB and the new U-eNB.

The method disclosed with reference to FIG. 31 in the second embodimentmay be applied to the process of releasing the last connected U-eNB.ST3101 to ST3115 of FIG. 31 can be applied. The sequence of configuringa new U-eNB and the sequence of releasing the last connected U-eNB maybe performed continuously or in parallel.

FIG. 61 shows an example sequence of the process [B] in FIG. 58.Disclosed below is a case in which the MME selects and determines a newU-plane establishing eNB (cell) (new U-eNB).

If the UE selects a cell different from the last connected C-eNB as anew C-plane establishing eNB (cell) (new C-eNB) in ST5815 of FIG. 58,the UE moves to the process [B]. In ST5816 of FIG. 61, the UE performsthe process of reestablishing RRC connection with the selected newC-eNB. After the completion of the RRC connection reestablishmentprocess in ST5816, the UE performs a service request process in ST6101to perform U-plane connection when needed. The RRC connection has beenestablished through the RRC connection reestablishment process ofST5816, and thus, the service request process of ST6101 does not requirethe RRC connection setup process. Through the service request of ST6101,the radio bearer 1 (3003) is reconfigured between the UE and the newC-eNB, and the S1 bearer 1 (3004) is reconfigured between the new C-eNBand the S-GW. This allows the U-plane data to be communicated betweenthe UE and the S-GW via the new C-eNB in ST3005 and ST3006.

Subsequent to the service request process of ST6101, in ST6001, the newC-eNB notifies the MME of a U-plane establishment request messagerequesting to start from the selection and determination of a U-planeonly establishing eNB (cell). The MME that has received the U-planeestablishment request message selects and determines a U-plane onlyestablishing eNB (cell) and determines the E-RAB configuration of eachof the eNBs (cells), to thereby configure/modify the E-RAB for each ofthe eNBs (cells). The processes disclosed with reference to ST3009 toST3036 in FIG. 30 are applied as the processes after these processes tothe process of configuring a U-plane only establishing eNB (cell). As aresult, the radio bearer 2 (DRB) is configured between the UE and thenew U-eNB and the S1 bearer 2 is configured between the new U-eNB andthe S-GW, allowing the U-plane data to be communicated between the UEand the S-GW via the new U-eNB.

As a result, the UE can perform communication using the new C-eNB andthe new U-eNB.

FIG. 62 shows an example sequence of the process [C] in FIG. 58.Disclosed below is a case in which the last connected C-eNB releases theU-plane establishing eNB. If the last connected C-eNB judges that thetimer T32 has expired in ST5825 of FIG. 58, the process moves to [C] andthe last connected C-eNB activates the process of disconnecting theconnection with the UE. As a result, the process of disconnecting theconnections between the UE and the last connected C-eNB and between theUE and the U-eNB is performed.

FIG. 62 shows a case in which the method disclosed in the thirdmodification of the second embodiment is applied as the process ofdisconnecting the connection with the UE by the last connected C-eNB.The processes of the sequence from ST3902 to ST3112 of FIG. 39 areapplied. However, the processes do not include the processes regardingthe signaling to the UE.

In ST3902, the last connected C-eNB determines to release all the eNBsthat establish U-plane including the own cell for the target UE. In thiscase, an indication that the process of disconnecting connection isperformed upon expiration of the timer T32 may be used as the criteriafor judgment. In ST3903, the last connected C-eNB notifies the MME of anE-RAB release request. In ST3010, the MME that has received the E-RABrelease request determines to release the E-RAB of each of the eNBsusing the identifier of a target UE, the identifier of the lastconnected C-eNB, the identifier of an eNB to be released, or the likeincluded in the request message. In ST6201, the MME notifies the lastconnected C-eNB of a message requesting to release the E-RAB release.The message requesting the E-RAB release, which is notified the lastconnected C-eNB from the MME, may include the information indicatingthat the bearer release is targeted for all the RB/S1 bearers. InST3102, the MME notifies the last connected U-eNB of the messagerequesting the E-RAB release. In ST6202, the last connected C-eNB thathas received the message requesting to release the E-RAB releases allthe RB/S1 bearers configured for the target UE and deletes theinformation about the UE. In ST6203, the UE that has completed theprocess of ST6202 notifies the MME of the completion of the E-RABrelease. In ST3103, the last connected U-eNB that has received themessage requesting to release the E-RAB releases the DRB/S1 bearerconfigured for the target UE and deletes the information about the UE.In ST3109, the UE that has completed the process of ST3103 notifies theMME of the completion of the E-RAB release.

As a result, the last connected C-eNB can disconnect the RRC connectionwith the UE and brings the condition with the UE to the RRC_Idle statein 6204. The last connected C-eNB and the last connected U-eNB releasethe resources for all the RB/S1 bearers and delete the information aboutthe UE. The process of disconnecting connection is accordinglycompleted.

The method disclosed in this embodiment allows the UE to avoidmaintaining unnecessary resources for U-plane connection even if thecommunication quality between the C-plane establishing eNB (cell) anditself degrades and communication is disabled. This improves radioresource use efficiency.

U-plane connection can be established/released by eliminating theambiguity in the process between the UE and the NW side, enabling normaldata communication.

Malfunctions can be reduced as a system.

The timer T32 or T33 of the last connected C-plane establishing eNB(cell) is not stopped in the RRC connection reestablishment processperformed from the UE to the new C-plane establishing eNB (cell).

The process of disconnecting the connection of the U-plane onlyestablishing eNB (cell) by the NW side is activated upon expiration ofthe timer T32 or T33 of the last connected C-plane establishing eNB(cell).

A problem may occur, in which the timing of configuring a new U-planeonly establishing eNB (cell) may differ from the timing of the processof disconnecting the connection of the U-plane only establishing eNB(cell) by the NW side.

To solve this problem, the MME makes adjustment.

When the process of disconnecting connection is activated uponexpiration of the timer T32 or T33, the MME that has received a U-planeconnection release request message checks whether a new C-planeestablishing eNB (cell) configures a U-plane only establishing eNB(cell) for the UE.

If the configuration above is performed, the MME discards the releaseprocess. If the configuration above is not performed, the MME performsthe release process.

As a result, an occurrence of such a problem that, for example, a newlyconfigured U-plane only establishing eNB (cell) is released can beprevented. This reduces malfunctions as a system, achieving a stableoperation.

The last connected C-plane establishing eNB (cell) may notify the MME ofthe information for reducing malfunctions in the judgment by the MME.

The information is included in a U-plane connection release requestmessage to be notified the MME from the last connected C-planeestablishing eNB (cell).

Three specific examples of the information will be disclosed below.

(1) Whether a release process request is made upon expiration of thetimer.

(2) The identifier of the last connected C-plane establishing eNB (cell)whose timer has expired.

(3) The identifier of a target UE.

In another method, the information as to whether the reconfiguration isperformed due to an RLF may be provided to prevent malfunctions in thejudgment by the MME. The information may be notified from the UE to theMME, from the UE to the new C-plane establishing eNB (cell), or from anew C-plane establishing eNB (cell) to the MME.

The MME can accordingly judge whether the configuration of the U-planeonly establishing eNB (cell) has configured due to an RLF. Thus, ifreceiving a U-plane connection release request message after theconfiguration of the U-plane only establishing eNB (cell) or if theconfiguration of the U-plane only establishing eNB (cell) is performeddue to an RLF, the MME may discard the U-plane connection releaserequest message. Or, if the configuration is not performed due to anRLF, the MME may perform the process of disconnecting (releasing) theU-plane only establishing eNB (cell) in accordance with the U-planeconnection release request message.

The use of the above-mentioned method can reduce malfunctions in thejudgment by the MME.

In another method of preventing a problem that the timing of configuringa new U-plane only establishing eNB (cell) may differ from the timing ofthe process of disconnecting the connection with the U-plane onlyestablishing eNB (cell) by the NW side, the signaling, which instructsthe last connected C-plane establishing eNB (cell), from the new C-planeestablishing eNB (cell), to end the process of disconnecting theconnection of the U-plane only establishing eNB upon expiration of thetimer T32 or T33 by the last connected C-plane establishing eNBtriggered by the RRC connection reestablishment process from the UE tothe new C-plane establishing eNB (cell), may be provided. The signalingmay be notified from the new C-plane establishing eNB (cell) to the lastconnected C-plane establishing eNB (cell) via the MME. For example, themethod is applied in the case where the U-plane only establishing eNB(cell), configured in the last connected C-plane establishing eNB, isthe same as the U-plane only establishing eNB (cell) to be configured inthe new C-plane establishing eNB (cell), preventing the U-plane onlyestablishing eNB (cell) from being released after the configuration.

The signaling may include the information about a U-plane onlyestablishing eNB (cell) to be configured by a new C-plane establishingeNB (cell), such as an identifier. This allows the last connectedC-plane establishing eNB (cell) to judge whether to end the process ofdisconnecting the connection of the U-plane only establishing eNB uponexpiration of the timer T32 or T33. Alternatively, the process ofdisconnecting the connection of only the same U-plane only establishingeNB (cell) may be ended.

As a result, malfunctions can be reduced as a system, achieving a stableoperation.

First Modification of Eighth Embodiment

<Processing Method (b) of Disconnecting Connection with U-Plane OnlyEstablishing eNB>

Another specific example of the processing method of disconnecting theconnection with a U-plane only establishing eNB (cell) will bedisclosed.

If detecting an RLF in the connection with the C-plane establishing eNB(cell), the UE disconnects the connection with the U-plane onlyestablishing eNB (cell).

As the process of disconnecting the connection with the U-plane onlyestablishing eNB (cell), the UE performs the process of disconnectingall the U-plane connections of all the U-plane only establishing eNBs(cells) connected with the UE. The UE releases all the U-plane radioresources including releasing of the MAC, RLC, and PDCP of all theU-plane RBs in all the U-plane only establishing eNBs (cells).

Part (b) of FIG. 57 is a diagram for describing an RLF-related processaccording to this modification. Part (b) of FIG. 57 is similar to part(a) of FIG. 57, and thus, the common description of the same elementswill not be described here.

The UE in the normal operation state performs RLM between the C-planeestablishing eNB (cell) and itself and, if having detected out-of-sync(radio problem detection) a predetermined number of times (N21) in arow, enters the first phase.

The UE continuously performs RLM between the C-plane establishing eNB(cell) and itself in the first phase and, if having detected in-sync apredetermined number of times (N22) in a row, returns to the normaloperation state. If not having detected in-sync the predetermined numberof times (N22) in a row within a predetermined period (T21) from theradio problem detection, the UE detects an RLF and enters the secondphase.

If detecting an RLF in the connection with the C-plane establishing eNB(cell), the UE disconnects the connection with the U-plane onlyestablishing eNB (cell).

In the second phase, the UE stores the RLF information and activates theRRC connection reestablishment process.

If AS security is not activated, the UE may perform the process ofleaving from RRC connection.

<RRC Connection Reestablishment Process>

In activating the RRC connection reestablishment process, the UE stopsall the RBs except for an SRB0 of the C-plane establishing eNB (cell)and, for example, resets the MAC, releases the SCell, applies thedefault PHY configuration, and applies the MAC main configuration. Then,the UE performs the cell selection process. If there is U-planeconnection between the UE and the C-plane establishing eNB (cell), theUE stops all the RBs for the U-plane connection as well. In other words,as for the U-plane connection with the C-plane establishing eNB (cell),the UE follows the process for the C-plane establishing eNB (cell), notthe process for the U-plane only establishing eNB (cell).

If carrier aggregation (CA) is configured in the U-plane onlyestablishing eNB (cell), the SCell in the CA may be released.

<Comparison with Eighth Embodiment>

Disclosed below is a method of handling a U-plane only establishing eNB(cell) when the UE performs the process of leaving from RRC connection(leaving RRC_Connected) or performs the RRC connection reestablishmentprocess.

Unlike the method disclosed in the eighth embodiment, when havingsucceeded cell selection in the second phase, the UE has disconnected(released) the connection with the U-plane only establishing eNB (cell).Thus, a new U-plane only establishing eNB (cell) is configured even ifthe UE selects any C-plane establishing eNB (cell) in cell selection orif the C-plane establishing eNB (cell) that has reestablished RRCconnection or the MME selects and determines any U-plane onlyestablishing eNB (cell).

Thus, it suffices that the MME configures the E-RAB of each of the eNBs(cells), and accordingly, the MME needs to be notified of the request toconfigure a U-plane only establishing eNB (cell).

The method of connecting with a different U-plane only establishing eNB(cell) when a last connected C-plane establishing eNB (cell) isselected, disclosed in the eighth embodiment, may be applied as themethod of configuring and releasing a U-plane only establishing eNB(cell) in this case.

Alternatively, the method in the case where a different C-planeestablishing eNB (cell) is selected, disclosed in the eighth embodiment,may be applied.

Compared with the method disclosed in the eighth embodiment, the methoddisclosed in this modification prevents the UE from unnecessarilymaintaining radio resources for U-plane connection also in the secondphase. In other words, the process of disconnecting the connection withthe U-plane only establishing eNB (cell) is performed at an early stage,improving radio resource use efficiency.

The second phase after the RLF is a phase in which the cell selectionprocess is performed. In other words, even if the communication isrecovered, the connection is highly likely to be the connection withanother cell (different C-plane establishing eNB (cell)). The connectionwith another cell may require the U-plane configuration according to thestatus of the connection with the cell. The UE performs, inconsideration the above, the process of disconnecting the connectionwith a U-plane only establishing eNB (cell) at the time of RFLdetection, so that the communication environment with a new C-planeestablishing eNB (cell) can be reflected. This prevents a decrease incommunication quality when an RRC connection is reestablished.

<Difference of Timing Between Configuration and Release>

The disconnection (release) of the U-plane only establishing eNB (cell)by the NW side in this modification is managed by the timer T31 in theRLF-related process by the C-plane establishing eNB (cell) such that theprocess of disconnecting connection is performed upon expiration of thetimer T31. The process of disconnecting connection may be performed dueto an RLF by the NW side as well as an RLF by the UE.

However, the process is not necessarily performed by the UE and the NWside at exactly the same timing.

The timer T31 of the last connected C-plane establishing eNB (cell)cannot be reset in the RRC connection reestablishment process from theUE to a new C-plane establishing eNB (cell).

The timing of configuring a new U-plane only establishing eNB (cell) maydiffer from the timing of releasing the U-plane only establishing eNB(cell) by the NW side.

In this case, such a problem that the newly configured U-plane onlyestablishing eNB (cell) is released may occur.

To solve this problem, the MME makes adjustment.

The method disclosed in the eighth embodiment may be applied as theadjustment method by the MME. Similar effects can be achieved.

The above-mentioned method reduces malfunctions in the judgment by theMME.

Second Modification of Eighth Embodiment

<Processing Method (c) of Disconnecting Connection with U-Plane OnlyEstablishing eNB>

Disclosed below is another specific example of the processing method ofdisconnecting the connection with a U-plane only establishing eNB(cell).

If detecting a radio problem in the connection with the C-planeestablishing eNB (cell), the UE disconnects the connection with theU-plane only establishing eNB (cell).

As the process of disconnecting the connection with the U-plane onlyestablishing eNB (cell), the UE performs the process of disconnectingall the U-plane connections of all the U-plane only establishing eNBs(cells) connected with the UE. The UE releases all the U-plane radioresources including releasing of the MAC, RLC, and PDCP of all theU-plane RBs in all the U-plane only establishing eNBs (cells).

Part (c) of FIG. 57 is a diagram illustrating an RLF-related processaccording to this modification. Part (c) of FIG. 57 is similar to part(a) of FIG. 57, and thus, the common description of the same elementswill not be described here.

The UE in the normal operation state performs RLM between the C-planeestablishing eNB (cell) and itself and, if having detected out-of-sync(radio problem detection) a predetermined number of times (N21) in arow, enters the first phase.

If detecting a radio problem in the connection with the C-planeestablishing eNB (cell), the UE disconnects the connection with theU-plane only establishing eNB (cell).

The UE continuously performs RLM between the C-plane establishing eNB(cell) and itself in the first phase and, if having detected in-sync apredetermined number of times (N22) in a row, returns to the normaloperation state. If not having detected in-sync the predetermined numberof times (N22) in a row within a predetermined period (T21) from theradio problem detection, the UE detects an RLF and enters the secondphase.

In the second phase, the UE stores the RLF information and activates theRRC connection reestablishment process.

If AS security is not activated, the UE may perform the process ofleaving from RRC connection.

<RRC Connection Reestablishment Process>

In activating the RRC connection reestablishment process, the UE stopsall the RBs except for an SRB0 of the C-plane establishing eNB (cell)and, for example, resets the MAC, releases the SCell, applies thedefault PHY configuration, and applies the MAC main configuration. Then,the UE performs the cell selection process. If there is U-planeconnection between the UE and the C-plane establishing eNB (cell), theUE stops all the RBs for the U-plane connection as well. In other words,as for the U-plane connection with the C-plane establishing eNB (cell),the UE follows the process for the C-plane establishing eNB (cell), notthe process for the U-plane only establishing eNB (cell).

If carrier aggregation (CA) is configured in the U-plane onlyestablishing eNB (cell), the SCell in the CA may be released.

<Comparison with First Modification of Eighth Embodiment>

The method disclosed in the first modification of the eighth embodimentmay be applied as the method of handling a U-plane only establishing eNB(cell) in the case where the UE performs the process of leaving from RRCconnection (leaving RRC_Connected) and in the case where the UE performsthe RRC connection reestablishment process. Similar effects can beachieved.

<Comparison with Eighth Embodiment and First Modification of EighthEmbodiment

Disclosed below is a method of handling a U-plane only establishing eNB(cell) when the UE detects a radio problem and then performsresynchronization (detects in-sync a predetermined number of times (N22)in a row) to return to the normal operation state.

Unlike the methods disclosed in the eighth embodiment and the firstmodification of the eighth embodiment, when performing resynchronizationin the first phase, the UE has disconnected (released) the connectionwith the U-plane only establishing eNB (cell). Thus, a new U-plane onlyestablishing eNB (cell) is configured even if the (last connected)C-plane establishing eNB (cell) with which the UE has resynchronized orthe MME selects and determines any U-plane only establishing eNB (cell).

Thus, it suffices that the MME configures the E-RAB of each of the eNBs(cells), and accordingly, the last connected C-plane establishing eNB(cell) needs to notify the MME of the request to configure a U-planeonly establishing eNB (cell).

The method of connecting with a different U-plane only establishing eNB(cell) when a last connected C-plane establishing eNB (cell) isselected, disclosed in the eighth embodiment, may be applied as themethod of configuring and releasing a U-plane only establishing eNB(cell) in this case.

The method disclosed in this modification enables the release ofresources at an earlier stage than in the eighth embodiment or the firstmodification of the eighth embodiment. Therefore, unnecessary resourcescan be eliminated in the case where, for example, recovery(resynchronization, RRC connection reestablishment) fails as aconsequence, improving resource use efficiency.

<Difference of Timing Between Configuration and Release>

The disconnection (release) of the U-plane only establishing eNB (cell)by the NW side in this modification may be performed when a radioproblem with the UE is detected in the RLF-related process by theC-plane establishing eNB (cell).

However, a radio problem is not necessarily detected by the UE and theNW side at exactly the same timing.

The process of disconnecting the connection of the U-plane onlyestablishing eNB (cell) by the NW side is activated in the detection ofa radio problem by the last connected C-plane establishing eNB (cell).

The timing of configuring the new U-plane only establishing eNB (cell)may differ from the timing of releasing the U-plane only establishingeNB (cell) by the NW side.

In this case, such a problem that the newly configured U-plane onlyestablishing eNB (cell) is released may occur.

To solve this problem, the MME makes adjustment.

When the connection release process is activated upon radio problemdetection, the MME checks whether it has configured a U-plane onlyestablishing eNB (cell) for the UE in the last connected C-planeestablishing eNB (cell).

If the configuration has been performed, the MME discards the releaseprocess. If the configuration has not been performed, the MME performsthe release process.

The last connected C-plane establishing eNB (cell) may notify the MME ofthe information for reducing malfunctions in the judgment by the MME.

The information is included in a release request message to be notifiedthe MME from the last connected C-plane establishing eNB (cell).

Three specific examples of the information will be disclosed below.

(1) Information indicative of whether a release process request is madeupon radio problem detection.

(2) The identifier of the last connected C-plane establishing eNB (cell)that has detected a radio problem.

(3) The identifier of a target UE.

In another method, the information as to whether the reconfigurationafter resynchronization is performed may be provided and notified toprevent malfunctions in the judgment by the MME. The information may benotified from the UE to the MME, from the UE to the last connectedC-plane establishing eNB (cell), or from the last connected C-planeestablishing eNB (cell) to the MME.

The MME can accordingly judge whether the configuration of the U-planeonly establishing eNB (cell) has been configured due toresynchronization. Thus, if receiving a release request message afterthe configuration of the U-plane only establishing eNB (cell) or if theconfiguration of the U-plane only establishing eNB (cell) is performeddue to resynchronization, the MME may discard the release requestmessage. Or, if the configuration is not performed due toresynchronization, the MME may perform the process of disconnecting(releasing) the connection of the U-plane only establishing eNB (cell)in accordance with the release request message.

The use of the above-mentioned method can reduce malfunctions in thejudgment by the MME.

In the eighth embodiment to the second modification of the eighthembodiment, to start the activation of the process of disconnecting theconnection of the U-plane only establishing eNB in the RLF-relatedprocess by the C-plane establishing eNB much later than the activationof the process of disconnecting the connection of the U-plane onlyestablishing eNB in the RLF-related process by the UE, the predeterminedperiod T31 configured in the RLF-related process by the C-planeestablishing eNB may be configured longer than the predetermined periodT21 configured in the RLF-related process by the UE, and/or may beconfigured longer than T22 if T32 is configured similarly, and/or may beconfigured longer than the sum of T21 and T22 if T33 is configured.

Thus, the activation of the process of disconnecting the connection ofthe U-plane only establishing eNB in the RLF-related process by theC-plane establishing eNB can be started much later than the activationof the process of disconnecting the connection of the U-plane onlyestablishing eNB in the RLF-related process by the UE. This reducesmalfunctions that, for example, the NW side first performs the processof disconnecting the connection of the U-plane only establishing eNBthough the UE has yet to perform the process of disconnecting theconnection of the U-plane only establishing eNB. The signalings, whichare associated with the process of disconnecting the connection of theU-plane only establishing eNB by the NW side, can be reduced.

<HOF>

The second embodiment to the first modification of the third embodimenthave disclosed that a U-plane only establishing eNB (cell) is changednot by HO but by addition/release/modification of a U-plane onlyestablishing eNB (cell). Meanwhile, it has been disclosed that HO may beapplied in changing a C-plane establishing cell. The method of handlinga U-plane only establishing cell in the case where HO is performedbetween C-plane establishing cells has also been disclosed.

It has been disclosed in (2) that the eNB that establishes U-planeconnection is notified from the target C-plane establishing eNB to theUE as the method of handling a U-plane only establishing cell in thecase where HO is performed between C-plane establishing cells.Alternatively, if the U-plane only establishing cell is the same beforeand after HO, the UE may not be notified of the eNB. If the UE is notnotified of the eNB in HO, the UE may need not to change the connectionof the U-plane only establishing cell.

As a result, the information about the U-plane only establishing cellneeds not to be transmitted to the UE from the target C-planeestablishing cell via the source C-plane establishing cell, reducing anamount of signaling or an amount of information included in the message.

In another method, if the U-plane only establishing cell is the samebefore and after HO, the UE may be notified of the informationindicating that the U-plane only establishing cell established beforeand after HO is the same. The information is transmitted to the UE fromthe target C-plane establishing cell via the source C-plane establishingcell. A small amount of information is required compared with theinformation about the U-plane only establishing eNB, reducing an amountof signaling or an amount of information included in a message.

Disclosed below are two methods of handling a U-plane only establishingcell when the UE detects a HO failure (HOF) in HO of the C-planeestablishing cell.

(1) When the UE detects a HOF of the C-plane establishing cell, theconnection with the U-plane only establishing eNB (cell) isdisconnected. The method disclosed in the eighth embodiment may beapplied as the method of disconnecting the connection with the U-planeonly establishing eNB (cell).

(2) When the UE detects a HOF of the C-plane establishing cell, the UEis considered to have detected an RLF, and the U-plane only establishingcell is handled as in the case where the UE detects an RLF. The methoddisclosed in the eighth embodiment or the first modification of theeighth embodiment may be applied as the method of handling a U-planeonly establishing cell when the UE detects an RLF.

When an RLF is detected in the HO procedure, it may be determined that aHOF is detected. Also in this case, the U-plane only establishing cellis handled as in the case where the UE detects an RLF.

As a result, for a HOF in the case where the UE communicates with aplurality of eNBs (cells), the method of handling a U-plane onlyestablishing eNB (cell) can be specified, enabling normal datacommunication. Also, malfunctions can be reduced as a system. Further,unnecessary resources can be prevented from being maintained for theconnection between the UE and the U-plane only establishing eNB (cell),improving radio resource use efficiency.

Ninth Embodiment

<RLF-Related Process of U-Plane Only Establishing eNB>

This embodiment will disclose another method of the RLF-related processin the case where the UE performs communication using a plurality ofdifferent eNBs (cells). The process will be referred to as theRLF-related process of the U-plane only establishing eNB (cell).

The UE performs RLM between the U-plane only establishing eNB (cell) anditself.

The UE performs the process of disconnecting the connection with theU-plane only establishing eNB (cell) in accordance with the connectionstatus of the U-plane only establishing eNB (cell).

Disclosed below are three processing methods of disconnecting theconnection with the U-plane only establishing eNB (cell).

(1) When detecting a radio problem in the connection with a U-plane onlyestablishing eNB (cell), the UE disconnects the connection with theU-plane only establishing eNB (cell).

(2) When detecting an RLF in the connection with a U-plane onlyestablishing eNB (cell), the UE disconnects the connection with theU-plane only establishing eNB (cell).

(3) When failing in reconnection in the connection with a U-plane onlyestablishing eNB (cell), the UE disconnects the connection with theU-plane only establishing eNB (cell).

In any of the methods, RLM and the RLF-related process are performed perU-plane only establishing eNB (cell) connected with the UE.

Part (a) of FIG. 63 is a diagram for describing an RLF-related processaccording to the method (1).

When the UE in the normal operation state has performed RLM of theU-plane only establishing eNB (cell) and has detected out-of-sync (radioproblem detection) a predetermined number of times (N41) in a row, theUE disconnects the connection with the U-plane only establishing eNB(cell). The out-of-sync of the U-plane only establishing eNB (cell) willbe described below.

This method allows the connection with the U-plane only establishing eNB(cell) to be disconnected at an earlier stage than the other twomethods. The radio resources for the U-plane only establishing eNB(cell) are accordingly not required to be maintained for a long period,improving radio resource use efficiency.

Part (b) FIG. 63 is a diagram for describing an RLF-related processaccording to the method (2).

Part (b) of FIG. 63 is similar to part (a) of FIG. 63, and thus, thecommon description of the same elements will not be described here.

The UE in the normal operation state performs RLM between the U-planeonly establishing eNB (cell) and itself and, when detecting out-of-sync(radio problem detection) a predetermined number of times (N41) in arow, shifts the connection status with the U-plane only establishing eNB(cell) to the first phase.

The UE continuously performs RLM between the U-plane only establishingeNB (cell) and itself in the first phase and, when detecting in-sync apredetermined number of times (N42) in a row, returns to the normaloperation state. When not detecting in-sync the predetermined number oftimes (N42) in a row within a predetermined period (T41) from the radioproblem detection, the UE detects an RLF and disconnects the connectionwith the U-plane only establishing eNB (cell). The in-sync of theU-plane only establishing eNB (cell) will be described below.

The method allows the UE to return to the normal operation state whengood communication quality is resumed in the first phase. Thus, theprocess of disconnecting connection needs not to be activated due totemporary degradation in communication quality, resulting in simplifiedcontrol, which reduces malfunctions.

Part (c) of FIG. 63 is a diagram for describing an RLF-related processaccording to the method (3).

Part (c) of FIG. 63 is similar to part (b) of FIG. 63, and thus, thecommon description of the same elements will not be described here.

The UE in the normal operation state performs RLM between the U-planeonly establishing eNB (cell) and itself and, when detecting out-of-sync(radio problem detection) a predetermined number of times (N41) in arow, shifts the connection status with the U-plane only establishing eNB(cell) to the first phase.

The UE continuously performs RLM between the U-plane only establishingeNB (cell) and itself in the first phase and, when detecting in-sync apredetermined number of times (N42) in a row, returns to the normaloperation state. When not detecting in-sync the predetermined number oftimes (N42) in a row within a predetermined period (T41) from the radioproblem detection, the UE detects an RLF and enters the second phase.

In the second phase, the UE activates the process of reconnecting withthe U-plane only establishing eNB (cell).

When succeeding in reconnection by the process of reconnecting with theU-plane only establishing eNB (cell) within the predetermined period(T42) from the RLF detection, the UE returns to the normal operationstate. When failing in reconnection within the predetermined period(T42) from the RLF detection, the UE disconnects the connection with theU-plane only establishing eNB (cell).

The reconnection process in the second phase may be performed on thesame U-plane only establishing eNB (cell) as the U-plane onlyestablishing eNB (cell) whose RLF has been detected.

Here, in the second phase, the connection with the U-plane onlyestablishing eNB (cell) is disconnected upon expiration of apredetermined period. Alternatively, in another method, a predeterminednumber of trial reconnections may be provided in the second phase and,if reconnection fails after the predetermined number of trialreconnections, the connection with the U-plane only establishing eNB(cell) may be disconnected. A specific example of this method has beendisclosed in the method of the second embodiment in which the UEperforms RLM with each of the U-plane establishing eNBs (cells) andreleases an eNB that has established U-plane only.

In activating the reconnection process, the UE may stop all the U-planeRBs of the U-plane only establishing eNB (cell). The method disclosed inthe eighth embodiment may be applied as the processing method. If the UEis still in the normal operation state, when the UE performs the processof reconnecting with the U-plane only establishing eNB (cell), controlbecomes complicated, increasing a risk of malfunctions. Such a problemcan be prevented here.

The method (3) needs not to activate the process of disconnectingconnection until it is judged that reconnection cannot be made, furthersimplifying control, which reduces malfunctions.

In the second phase, the UE may be allowed to perform the process ofreconnecting with a U-plane only establishing eNB (cell) different fromthe U-plane only establishing eNB (cell) whose RLF has been detected. Inthis case, the C-plane establishing eNB (cell) or the MME may select anddetermine a new U-plane only establishing eNB (cell) to configure it forthe UE. In this case, the methods of the second embodiment and the thirdmodification of the second embodiment are applicable.

When judging to disconnect the connection with the U-plane onlyestablishing eNB (cell) in the RLF-related process, the UE disconnectsthe connection with the U-plane only establishing eNB (cell).

Disclosed below are two processing methods of disconnecting theconnection with the U-plane only establishing eNB (cell) by the NW side.

(1) Upon the UE notifying the C-plane establishing eNB (cell) of arequest to disconnect the connection with the U-plane only establishingeNB (cell), the disconnection process by the NW side is performed. Thedegradation in reception quality may be notified as a request todisconnect connection.

A specific example of this method has been disclosed in the method ofthe second embodiment in which the UE performs RLM with each of theU-plane establishing eNBs (cells) and releases an eNB that hasestablished U-plane only.

(2) The disconnection process by the NW side is performed in accordancewith the RLF-related process by the U-plane only establishing eNB(cell).

The RLF-related processes by the C-plane establishing eNB (cell),disclosed in the eighth embodiment to the second modification of theeighth embodiment, are applicable as the RLF-related process by theU-plane only establishing eNB (cell) on the NW side. The processperformed by the C-plane establishing eNB (cell) may be performed by theU-plane only establishing eNB (cell).

When the method (1) is used as the processing method of disconnectingthe connection with the U-plane only establishing eNB (cell), theRLF-related process by the C-plane establishing eNB (cell), disclosed inthe second modification of the eighth embodiment, may be applied. Whenthe U-plane only establishing eNB (cell) detects a radio problem in theconnection with the UE, the U-plane only establishing eNB (cell)notifies the MME of a request to disconnect connection. The messagerequesting to disconnect connection may be notified via the C-planeestablishing eNB (cell). The degradation in reception quality may benotified as the request to disconnect connection.

When the method (2) is used as the processing method of disconnectingthe connection with the U-plane only establishing eNB (cell), theRLF-related process by the C-plane establishing eNB (cell), disclosed inthe first modification of the eighth embodiment, may be applied. Whenthe U-plane only establishing eNB (cell) detects an RLF in theconnection with the UE, the U-plane only establishing eNB (cell)notifies the MME of a request to disconnect connection. The messagerequesting to disconnect connection may be notified via the C-planeestablishing eNB (cell). The degradation in reception quality may benotified as the request to disconnect connection.

When the method (3) is used as the processing method of disconnectingthe connection with the U-plane only establishing eNB (cell), theRLF-related process by the C-plane establishing eNB (cell), disclosed inthe eighth embodiment, may be applied. When the U-plane onlyestablishing eNB (cell) judges that the timer T32 has expired or thetimer T33 has expired in the connection with the UE, the U-plane onlyestablishing eNB (cell) notifies the MME of a request to disconnectconnection. The message requesting to disconnect connection may benotified via the C-plane establishing eNB (cell). The degradation inreception quality may be notified as the request to disconnectconnection.

The processes of disconnecting the connection with the U-plane onlyestablishing eNB (cell) performed using a data monitoring timer,disclosed in the second embodiment, the third modification of the secondembodiment, and the third embodiment, are applicable to this method. Asa specific example, in the sequences of FIG. 32, FIG. 40, FIG. 41, andFIG. 46, the sequence of performing the U-plane disconnection (release)process upon expiration of the data monitoring timer in the U-eNB (cell)may be applied.

In the process when reconnection is enabled by the process ofreconnecting with the U-plane only establishing eNB (cell), radioresources stopped in the activation of the reconnection process arerestarted, and the normal operation is resumed.

There is no change in the configuration of the DRB bearer, theconfiguration of the S1 bearer, and the path configuration by theU-plane only establishing eNB (cell) until the U-plane only establishingeNB (cell) is reconfigured or the connection thereof is disconnected.Each node accordingly keeps the original configuration, and thus canperform reconnection using the original configuration.

FIG. 64 shows an example sequence of an RLF-related process by theU-plane only establishing cell according to the ninth embodiment, whichshows a case in which the method (3) is used as the processing method ofdisconnecting the connection with the U-plane only establishing eNB(cell). The RLF-related process by the UE and the RLF-related process bythe U-plane only establishing cell are shown together.

In ST6401, the UE that has started the connection with the U-eNB startsRLM with the U-eNB. In ST6402, the UE judges whether out-of-sync hasoccurred N41 times in a row in the connection with the U-eNB. Ifout-of-sync has occurred N41 times in a row, the UE detects a radioproblem (ST6403) to shift to the first phase. If out-of-sync has notoccurred N41 times in a row, the UE performs RLM and again performsST6402. In ST6404, the UE that has detected a radio problem in ST6403starts a timer T41. The UE continuously performs RLM in the first phase.In ST6405, the UE judges whether in-sync has occurred N42 times in arow. If in-sync has occurred N42 times in a row, the UE returns to thenormal operation to perform RLM, and then performs ST6402. If in-synchas not occurred N42 times in a row, in ST6406, the UE judges whetherthe timer T41 has expired. If the timer T41 has not expired, the UEcontinuously performs RLM and then performs ST6405. If the timer hasexpired, the UE detects an RLF in ST6407. In ST6408, the UE that hasdetected an RLF in ST6407 enters a second phase, and stops the timer T41and starts the timer T42. In ST6409, the UE stops the RB with theU-plane only establishing cell (eNB). In the second phase, the UEactivates the process of reconnecting with the U-eNB to reconnecttherewith (ST6410). In ST6411, the UE judges whether it has succeeded inreconnection and, if it has failed in reconnection, judges whether thetimer T42 has expired in ST6412. If the timer T42 has not expired, theUE continuously performs the process of reconnecting with the U-eNB inST6410. If the timer T42 has expired in ST6412, the UE performs theprocess of disconnecting the connection with the U-eNB in ST6413.

If the UE is successfully reconnected with the U-eNB in ST6411, the UEstops the timer T42 in ST6414 and, in ST6415, restarts the stopped RB ofthe U-eNB. As a result, the connection with the U-eNB enters the normaloperation, allowing the radio bearer 2 (DRB) (3027) and the S1 bearer 2(3028) to be continuously configured between the UE and the U-eNB (lastconnected U-eNB) and between the U-eNB and the S-GW, respectively. TheU-plane data can be accordingly communicated between the UE and the S-GWvia the U-eNB in ST3032 and ST3033.

Next, the RLF-related process by the U-eNB will be described.

In ST6416, the U-eNB that is in U-plane connection with the UE startsRLM between the UE and itself. In ST6417, the U-eNB judges whether anuplink signal or channel has been undelivered N31 times in a row in theconnection with the UE. The uplink signal may be, for example, aperiodic CQI. If a periodic CQI has been undelivered N31 times in a row,the U-eNB detects a radio problem (ST6418). If a periodic CQI has notbeen undelivered N31 times in a row, the U-eNB performs RLM and againperforms ST6417. In ST6419, the U-eNB that has detected a radio problemstarts the timer T31 and continuously performs RLM. In ST6420, the U-eNBjudges whether it has successfully received a periodic CQI N32 times ina row. If having successfully received a periodic CQI N32 times in arow, the U-eNB returns to the normal operation to perform RLM andperforms ST6417. If having failed in receiving a periodic CQI N32 timesin a row, in ST6421, the U-eNB judges whether the timer T31 has expired.If the timer T31 has not expired, the U-eNB continuously performs RLMand performs ST6420. If the timer has expired, the U-eNB detects an RLFin ST6422. In ST6423, the U-eNB that has received an RLF in ST6422 stopsthe timer T31 and starts the timer T32. The U-eNB that has detected anRLF performs the reconnection process shown in ST6410 between the UE anditself. In ST6424, the U-eNB judges whether the reconnection with the UEis complete. If the reconnection is complete, the U-eNB stops the timerT32 in ST6425. Thus, the connection with the UE enters the normaloperation, and the radio bearer 2 (DRB) (3027) and the S1 bearer 2(3028) are continuously configured between the UE and the U-eNB (lastconnected U-eNB) and between the U-eNB and the S-GW, allowing theU-plane data to be communicated between the UE and the S-GW via theU-eNB in ST3032 and ST3033.

If the reconnection with the UE is not complete in ST6424, in ST6426,the U-eNB judges whether the timer T32 has expired. If the timer has notexpired, the U-eNB again performs the reconnection process from the UE.If the timer has expired, the U-eNB performs the process of releasing aU-eNB upon expiration of the timer, shown in ST3203 to ST3115 of FIG.32. The process of disconnecting the connection with a U-eNB to bereleased in ST3106 included in ST3114 in FIG. 32 may be skipped if ithas been performed in ST6413.

As a result, the process of disconnecting the connection between the UEand the U-eNB is performed.

The method disclosed in this embodiment prevents a situation in whichthe connection with the U-plane only establishing eNB (cell) is kept.

Thus, radio resources will not be maintained unnecessarily, improvingradio resource use efficiency.

The ambiguity in the operations of the UE and the NW side is eliminated,reducing malfunctions as a system.

The RLM method has been disclosed in the second embodiment, which willbe disclosed here in greater detail.

The second embodiment has disclosed, as (1) to (4), that the RSreception result of each U-plane only establishing eNB (cell) is usedfor RLM. Alternatively, CSI-RS may be used. They may be used incombination.

The reception quality of the PDCCH may be evaluated as RLM.

The UE evaluates the PDCCH reception quality of the cell for U-planeonly connection. The UE associates the PDCCH reception quality with theRS reception quality (such as RSRP or RSRQ) in advance. The UE measuresthe RS reception quality of the cell for U-plane only connection, andevaluates the PDCCH reception quality of the cell based on theassociation.

Two predetermined thresholds are provided for the reception quality,where the case in which the PDCCH reception quality is not less than onepredetermined threshold is judged as in-sync, while the case in whichthe PDCCH reception quality is not greater than the other predeterminedthreshold is judged as out-of-sync.

The method of evaluating the PDCCH reception quality as the RLM of thecell for U-plane only connection can be controlled as with theconventional RLM, leading to simplified control.

The ePDCCH reception quality may be evaluated as RLM.

The UE evaluates the ePDCCH reception quality of the cell for U-planeonly connection.

The UE associates the ePDCCH reception quality with the receptionquality (such as RSRP or RSRQ) of the RS used in ePDCCH and/or the RSused in a subframe that uses ePDCCH in advance.

The UE measures the reception quality of the RS used in ePDCCH and/orthe RS used in a subframe that uses ePDCCH of the cell for U-plane onlyconnection, to thereby evaluate the ePDCCH reception quality of the cellbased on the association.

Two predetermined thresholds are provided for the reception quality,where the case in which the ePDCCH reception quality is not less thanone predetermined threshold is judged as in-sync and the case in whichthe ePDCCH reception quality is not greater than the other predeterminedthreshold is judged as out-of-sync.

Such a use of the ePDCCH reception quality in RLM is also applicable tothe case in which the ePDCCH is used. Application to the case where itis difficult to use the PDCCH allows RLM to be performed reliably.

First Modification of Ninth Embodiment

<Coordination Between RLF of C-Plane Establishing Cell and RLF ofU-Plane Only Establishing Cell>

When the UE is in connection with the C-plane establishing eNB and oneor a plurality of U-plane only establishing eNBs, the method for theRLF-related process by the C-plane establishing eNB, disclosed in theeighth embodiment, may be combined with the method for the RLF-relatedprocess by the U-plane only establishing eNB, disclosed in the ninthembodiment.

When the connection with the U-plane only establishing eNB isdisconnected in the RLF-related process by the C-plane establishing eNB,connection is disconnected irrespective of the connection status of eachof the U-plane only establishing eNBs in the RLF-related process by eachof the U-plane only establishing eNBs.

When the UE moves to RRC_Idle, accordingly, there is no connection withthe U-plane only establishing eNB. Such a state that the UE, which is inRRC_Idle, is in only U-plane connection can be eliminated.

While the connection with the U-plane only establishing eNB is yet to bedisconnected in the RLF-related process by the C-plane establishing eNB,the UE may follow the connection status of each of the U-plane onlyestablishing eNBs in the RLF-related process by each of the U-plane onlyestablishing eNBs.

This allows the UE to perform connection according to the connectionstatus per U-plane only establishing eNB. Unnecessary connection withthe U-plane only establishing eNB can be accordingly eliminated,improving radio resource use efficiency.

The connection status of the C-plane establishing cell may not depend onthe connection status of the U-plane only establishing cell.

The UE performs RRC connection by the C-plane establishing cell. Thus,if the connection status of the C-plane establishing cell does notdepend on the connection status of the U-plane only establishing cell,the UE can stably perform RRC connection. For example, even when the UEmoves and the communication quality of each of the U-plane onlyestablishing cells varies incessantly, the RLF-related process followsthe quality of the communication with one C-plane establishing cell.This enables stable RRC connection, firmly controlling UE movement.

Tenth Embodiment

<Small Cell Cluster>

The first embodiment to the first modification of the ninth embodimenthave disclosed the method in which a UE performs communication using aplurality of eNBs (cells) for one communication.

As a system, a plurality of eNBs may be handled as one group forsimplified control and a reduced amount of signaling. This embodimentwill disclose the method of handling a plurality of eNBs as one group.

The following four will disclose a plurality of eNBs to be handled asone group.

(1) A group of eNBs in a specific area.

(2) A group of a plurality of eNBs controlled by one concentratedcontrol node (concentrator).

(3) A group of eNBs belonging to the same frequency layer.

(4) Combination of (1) to (3).

The group may be referred to as a group or a cluster. For example, thegroup may be referred to as an eNB group or a node cluster. If the eNBsin a group are small cells, the group may be referred to as a small cellgroup or a small cell cluster.

In (1), the eNBs in a specific area are handled as one group,simplifying communication control in the specific area. For example, theeNBs in a specific area, disclosed in the first embodiment, may beequivalent to the above-mentioned eNBs.

In (2), one concentrated control node may be provided for a group of aplurality of eNBs handled as one group. In (2), a plurality of eNBs canbe controlled in a concentrated manner, simplifying control. For a smallcell group, a macro cell positionally overlaid on the small cell groupmay be a concentrator. Alternatively, a concentrator may be disposedindependently from a macro cell. Still alternatively, scheduling may beperformed independent of the macro cell. For example, the eNB forcentralized control and the target eNB for centralized control,disclosed in the first modification of the third embodiment, areequivalent to the above-mentioned eNBs.

In (3), a carrier in which the eNBs in a group have the same carrierfrequency is configured. In other words, the eNBs operate in the samefrequency layer. This simplifies a cell change in a group.

FIG. 65 is a diagram illustrating the case in which a plurality of eNBsare handled as one group.

Part (a) of FIG. 65 is a diagram illustrating the case in which aplurality of eNBs, which are handled as one group, constitute a group ofeNBs in a specific area. 6501 denotes a macro cell; 6502, the coverageconfigured by the macro cell; 6506, a small cell; and 6503, the coverageconfigured by the small cell. There are a plurality of small cells. 6504denotes a specific area. 6505 denotes a small cell group. The smallcells (6506) in the specific area (6504) are handled as the small cellgroup (6505).

Part (b) of FIG. 65 is a diagram illustrating the case in which aplurality of eNBs, which are handled as one group, constitute a group ofeNBs controlled by a concentrator. The same elements as part (a) of FIG.65 will be denoted by the same numbers and will not be described here.6507 denotes a concentrator. A group of the small cells (6506)controlled by the concentrator (6507) is handled as the small cell group(6505).

Part (c) of FIG. 65 is a diagram illustrating the case in which aplurality of eNBs, which are handled as one group, constitute a group ofeNBs belonging to the same frequency layer. The same elements as part(a) of FIG. 65 will be denoted by the same numbers and will not bedescribed here. The carrier frequency of a carrier configured by themacro cell is F1. A group of the small cells (6506) configuring thecarrier having a carrier frequency Fm is handled as the small cell group(6505).

Disclosed below is a configuration method in the case where a pluralityof eNBs are handled as a group, for example, a small cell group in eachof the embodiments.

The configuration information of a small cell group may be theidentifier of a small cell group, the identifier of the cell in thesmall cell group, or the like. The configuration information may includethe system information common to small cells or the system informationdedicated to each small cell. The configuration information may includethe frequency carrier of the cell in the small cell group or theidentifier of a concentrator if the concentrator is provided.

In the first embodiment, the cells to be selected in cell selection bythe UE may be limited to ones in a predetermined small cell group.

For cell selection, the configuration information of the small cellgroup may be notified the UE from the cell being in RRC-connectiontherewith in advance through RRC signaling. The configurationinformation may be included in one message. A new message may beprovided or the configuration information may be included in an existingRRC message to be notified. An RRC connection reconfiguration messagemay be used as a specific example of the existing RRC message. Theconfiguration information of the small cell group may be included inRadioResourceConfigDedicated information of the RRC connectionreconfiguration message.

In the second embodiment to the third embodiment, the U-planeestablishing cells or the U-plane only establishing cells, which areconfigured for the UE by the MME or the C-plane establishing cell, maybe configured as a small cell group. Although the second embodiment hasdisclosed the method in which a DRB list is used, the list may be a listof cells of a small cell group.

The cells, which are configured for the UE by the MME or the cell to beRRC-connected with the UE, may be limited to ones in a predeterminedsmall cell group in the sixth embodiment. The UE may be notified of theconfiguration information of a small cell group through RRC signaling.Alternatively, the UE may be notified of a cell to be activated ordeactivated in a small cell group through MAC signaling.

The UE performs configuration for the small cell in the small cellgroup, which has been notified through RRC signaling, and performscommunication with the small cell whose activation has been notifiedthrough MAC signaling.

A plurality of eNBs are configured as one group for the UE as describedabove, eliminating the need for individually notifying the UE of theconfigurations of the plurality eNBs a plurality of times through RRCsignaling.

In the case where a group of a plurality of eNBs is handled as onegroup, the list of identifiers of the groups may be provided asconfiguration information to be notified the UE through RRC signaling.In the case where a plurality of groups are configured, listing ofidentifiers leads to a reduction in overhead in signaling.

Disclosed below is a measurement method in the case where a group of aplurality of eNBs is handled as, for example, a small cell group in eachof the embodiments.

Radio resource management (RRM) will be disclosed. Cells in the samefrequency layer may be measured as the measurement of neighbor cells.

For example, a group of small cells belonging to the same frequencylayer is a small cell group, other frequency particularly needs not tobe measured when the small cell in the group is changed. Thus, limitingthe RRM measurement target to the cells in the same frequency layersimplifies the measurement process by the UE, allowing the measurementto be performed in a short period of time with low power consumption.

The RRM measurement target may be limited to the cells in a small cellgroup. The CRS of the cell in a small cell group may be measured. In thecase where a small cell is changed in the group, cells out of the groupneed not to be measured. Thus, limiting the RRM measurement to the cellsin a predetermined small cell simplifies the measurement process by theUE, allowing the measurement to be performed in a short period of timewith low power consumption.

The eNB (cell) in RRC connection notifies the UE of a measurementconfiguration of RRM measurement. The measurement configuration includesthe information indicating that measurement is performed in thefrequency layer of a predetermined small cell group. For example, thefrequency information to be measured may be included.

The measurement configuration may include the information indicatingthat a predetermined small cell group is measured. For example, theidentifier of the small cell group to be measured may be included. Theuse of the identifier together with the configuration information of thesmall cell group allows the cell in the small cell group being ameasurement target to be identified. This eliminates the need fordedicatedly including information per cell being a measurement target inthe measurement configuration, reducing an amount of information in themessage.

The measurement for a CQI/CSI report will be disclosed.

An activated cell may be measured. In this case, it is not necessary tomeasure a deactivated cell. Also in this case, the concentrator in asmall cell group may determine a cell to be activated/deactivated by RRMmeasurement. CSI-RS or CRS may be measured as the measurement for aCQI/CSI report.

The measurement method is configured in accordance with how a group ishandled as described above, simplifying a measurement process.

In the case where a group of a plurality of eNBs is handled as a groupsuch as a small cell group in each of the embodiments, the resource forconfiguring an RB/S1 bearer and the information for connection may bethe same in the each of the eNBs of the small cell group. For example,the UE context may be the same.

In communication using a C-plane establishing eNB and a U-plane onlyestablishing eNB, the resource for configuring a DRB/S1 bearer and theinformation for connection may be the same in all the U-plane onlyestablishing eNBs.

Particularly in the first modification of the third embodiment, the eNBfor centralized control may perform the same control and management onthe target eNBs for the target eNBs for centralized control. The eNB forcentralized control controls the target eNBs for centralized control,enabling easy control and management.

Consequently, the UE needs not to receive the resource information forconfiguring a bearer per eNB for all the eNBs in a small cell group orthe information for connection. One piece of information may be receivedas a small cell group. This reduces an amount of signaling or an amountof information of a message and simplifies control.

Eleventh Embodiment

<CA+Cell Aggregation>

This embodiment will disclose a method of further increasingcommunication capacity.

The UE performs communication using a plurality of eNBs (cells) for onecommunication and performs carrier aggregation (CA) in one or some eNBs(cells) of the plurality of eNBs (cells).

As a specific example, the UE performs communication using a macro celland a plurality of small cells positionally overlaid on the macro celland performs CA in the macro cell.

As another specific example, the UE performs communication using a macrocell and a plurality of small cells positionally overlaid on the macrocell and performs CA for the macro cell and the small cells.

As still another example, the UE performs communication using a C-planeestablishing cell and a U-plane only establishing cell and performs CAin the U-plane only establishing cell.

A scheduler needs to be shared in CA, and thus, a concentrator may beprovided which controls a plurality of eNBs (cells) for use in onecommunication in a concentrated manner.

FIG. 66 is a diagram illustrating the case in which communication isperformed using a macro cell and a plurality of small cells positionallyoverlaid on the macro cell and CA is performed in the macro cell. 6601denotes a UE, 6602 denotes a component carrier (CC) configured for theUE (6601) by the macro cell, and 6603, 6604, and 6605 denote carriersconfigured by a small cell #1, a small cell #2, and a small cell #3,respectively. The macro cell configures a CC1 having a carrier frequencyF1, a CC2 having a carrier frequency F2, and a CC3 having a carrierfrequency F3 for the UE (6601). The carrier frequencies of the smallcells #1, #2, and #3 are denoted by Fm. The UE (6601) performscommunication using the macro cell (6602), the small cell #1 (6603), thesmall cell #2 (6604), and the small cell #3 (6605) and performs CA usingthe CC1, the CC2, and the CC3 in the macro cell (6602).

Disclosed below is a method in which a UE recognizes the configurationinformation required for the UE to perform communication using aplurality of eNBs (cells) and perform CA in one or some eNBs (cells) ofthe plurality of eNBs (cells).

The PCell notifies the UE of the configuration information. Theconfiguration information may be the CA configuration information or theconfiguration information of an eNB (cell) that performs communication.If there are a plurality of PCells, the plurality of PCells may notifythe UE of the configuration information. The configuration informationmay be divided to be notified from a plurality of PCells to the UE.Alternatively, one PCell may notify the UE of the configurationinformation. One PCell may be a PCell that configures CA. One PCell maybe a cell that notifies the configuration for performing communicationusing a plurality of eNBs (cells).

In the example in which CA is performed using a cell without RRCconnection, such as CA performed in a U-plane only establishing cellamong the specific examples described above, the UE may be notified ofthe configuration information from the cell that is RRC-connected withthe UE being a CA target. The cell, which is RRC-connected with the UEbeing a CA target, may be a PCell. In this case, the cell without RRCconnection may notify the cell that is RRC-connected of theconfiguration information in advance. As a specific example, the U-planeonly establishing cell may notify the C-plane establishing cell of theconfiguration information as disclosed in the second embodiment. TheU-plane only establishing cell may notify the UE of the configurationinformation via the C-plane establishing cell.

Examples of the CA configuration information include the identifier ofthe eNB (cell) that performs CA, the carrier frequency information of acomponent carrier that configures CA, and the CC system information.

The information disclosed in the first embodiment to the tenthembodiment may be applied as the configuration information forperforming communication using a plurality of eNBs (cells). The methodof handling a plurality of eNBs as one group, disclosed in the tenthembodiment, may be applied. For example, the configuration informationmay be the identifier of the group, the identifier of each eNB in thegroup, or the system information of each eNB in the group.

Although the PCell notifies the UE of the configuration information, inanother method, the C-plane establishing cell may notify the UE of theconfiguration information. This method is effective in the case where CAis performed in a U-plane only establishing cell. The U-plane onlyestablishing cell may notify the C-plane establishing cell of theconfiguration information in advance. The U-plane only establishing cellmay notify the UE of the configuration information via the C-planeestablishing cell.

The configuration information may be notified the UE through RRCsignaling.

One message, which includes the configuration information composed ofthe CA configuration information and the configuration information of aneNB (cell) that performs communication, may be provided so that themessage is notified through RRC signaling. This reduces an amount ofsignaling.

Alternatively, the CA configuration information and the configurationinformation of an eNB (cell) that performs communication may be providedas individual messages to be notified through RRC signaling. As aresult, the case in which CA only needs to be configured or the case inwhich a plurality of eNBs only need to be configured can be handled.

These may be used while being appropriately combined.

In CA, the MAC activates/deactivates each of the CCs and theactivation/deactivation of each of the CCs are notified the UE throughMAC signaling. A plurality of eNBs may be treated similarly. The MACactivates/deactivates each of the eNBs configured in RRC and notifiesthe UE of the activation/deactivation of each eNB through MAC signaling.The UE may configure a radio resource for the eNB notified through RRCsignaling and perform communication with only the eNB activated throughMAC signaling. The UE may receive the PDCCH or ePDCCH of the activatedeNB to obtain scheduling information.

The eNBs to be used in communication and the CCs that constitute CA maybe provided with serial numbers, and the numbers and the information ofassociation between the number and each of the eNBs and the CCs may beincluded as the configuration information notified the UE through RRCsignaling. This allows for control based on the information whose amountis smaller than in the case where the identifiers of cells such as eNBsare used.

The MAC may collectively notify the UE of activation/deactivation of theeNBs to be used in communication and CCs that constitute CA. Thisreduces overhead of MAC signaling more than in the case where the MACnotifies separately. In this case, the serial numbers may be used toinstruct the eNB to be used in communication and CCs that constitute CA.This can reduce an amount of information of signaling.

The methods disclosed in the first embodiment to the tenth embodimentmay be appropriately applied as the communication method using aplurality of cells.

The embodiments and their modifications are merely illustrations of thepresent invention, and the embodiments and their modifications can becombined freely within the scope of the present invention. Thecomponents of the embodiments and their modifications can beappropriately changed or omitted. Therefore, high communication capacitycan be achieved by the installation of small eNBs (cells), and acommunication system capable of changing a cell during communicationwithout any load on a network can be provided.

1. (canceled)
 2. A mobile communication system in which a first basestation and a second base station communicate with a user equipment inparallel and the first base station and the second base stationcommunicate with a radio network controller in parallel, wherein in acontrol plane, the first base station communicates with the userequipment and the first base station communicates with the radio networkcontroller, and in a user plane, the second base station communicateswith the user equipment and the second base station communicates withthe radio network controller.
 3. The mobile communication systemaccording to claim 2, wherein in the user plane, the second base stationcommunicates directly with the radio network controller.
 4. The mobilecommunication system according to claim 2, wherein in the user plane,the first base station communicates directly with the user equipment andthe second base station communicates with the radio network controllervia the first base station.
 5. The mobile communication system accordingto claim 4, wherein the first base station distributes, to the userequipment and the second base station, data received from the radionetwork controller and transmits distributed data to the user equipmentand the second base station.
 6. The mobile communication systemaccording to claim 4, wherein the first base station rearranges theorder of data received from the user equipment and data received fromthe second base station and transmits rearranged data to the radionetwork controller.
 7. The mobile communication system according toclaim 2, wherein the radio network controller that communicates with thefirst base station in the control plane is a mobility management device.8. The mobile communication system according to claim 2, wherein theradio network controller that communicates with the second base stationin the user plane is a gateway station.
 9. A radio network controllerthat communicates with a first base station and a second base station inparallel, the first base station and the second base stationcommunicating with a user equipment in parallel, wherein in a controlplane, the radio network controller communicates with the first basestation that communicates with the user equipment, and in a user plane,the radio network controller communicates with the second base stationthat communicates with the user equipment.
 10. A base station thatcommunicates with a user equipment in parallel with another base stationand communicates with a radio network controller in parallel with theother base station, wherein in a control plane, the base stationcommunicates with the user equipment and the radio network controller,and in a user plane, the other base station communicates with the userequipment and the other base station communicates with the radio networkcontroller.
 11. A base station that communicates with a user equipmentin parallel with another base station and communicates with a radionetwork controller in parallel with the other base station, wherein in acontrol plane, the other base station communicates with the userequipment and the other base station communicates with the radio networkcontroller, and in a user plane, the base station communicates with theuser equipment and the radio network controller.
 12. A user equipmentthat communicates with a first base station and a second base station inparallel, the first base station and the second base stationcommunicating with a radio network controller, wherein in a controlplane, the user equipment communicates with the first base station thatcommunicates with the radio network controller, and in a user plane, theuser equipment communicates with the second base station thatcommunicates with the radio network controller.